intel_th: msu: Fix unused variable warning on arm64 platform

Commit ba39bd83 ("intel_th: msu: Switch over to scatterlist")
introduced the following warnings on non-x86 architectures, as a result
of reordering the multi mode buffer allocation sequence:

> drivers/hwtracing/intel_th/msu.c: In function ‘msc_buffer_win_alloc’:
> drivers/hwtracing/intel_th/msu.c:783:21: warning: unused variable ‘i’
> [-Wunused-variable]
> int ret = -ENOMEM, i;
>                    ^
> drivers/hwtracing/intel_th/msu.c: In function ‘msc_buffer_win_free’:
> drivers/hwtracing/intel_th/msu.c:863:6: warning: unused variable ‘i’
> [-Wunused-variable]
> int i;
>     ^

Fix this compiler warning by factoring out set_memory sequences and making
them x86-only.
Suggested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Fixes: ba39bd83 ("intel_th: msu: Switch over to scatterlist")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190621161930.60785-2-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/intel_th/msu.c

@@ -767,6 +767,30 @@ static int __msc_buffer_win_alloc(struct msc_window *win,
 	return -ENOMEM;
 }
 
+#ifdef CONFIG_X86
+static void msc_buffer_set_uc(struct msc_window *win, unsigned int nr_blocks)
+{
+	int i;
+
+	for (i = 0; i < nr_blocks; i++)
+		/* Set the page as uncached */
+		set_memory_uc((unsigned long)msc_win_block(win, i), 1);
+}
+
+static void msc_buffer_set_wb(struct msc_window *win)
+{
+	int i;
+
+	for (i = 0; i < win->nr_blocks; i++)
+		/* Reset the page to write-back */
+		set_memory_wb((unsigned long)msc_win_block(win, i), 1);
+}
+#else /* !X86 */
+static inline void
+msc_buffer_set_uc(struct msc_window *win, unsigned int nr_blocks) {}
+static inline void msc_buffer_set_wb(struct msc_window *win) {}
+#endif /* CONFIG_X86 */
+
 /**
  * msc_buffer_win_alloc() - alloc a window for a multiblock mode
  * @msc:	MSC device
@@ -780,7 +804,7 @@ static int __msc_buffer_win_alloc(struct msc_window *win,
 static int msc_buffer_win_alloc(struct msc *msc, unsigned int nr_blocks)
 {
 	struct msc_window *win;
-	int ret = -ENOMEM, i;
+	int ret = -ENOMEM;
 
 	if (!nr_blocks)
 		return 0;
@@ -811,11 +835,7 @@ static int msc_buffer_win_alloc(struct msc *msc, unsigned int nr_blocks)
 	if (ret < 0)
 		goto err_nomem;
 
-#ifdef CONFIG_X86
-	for (i = 0; i < ret; i++)
-		/* Set the page as uncached */
-		set_memory_uc((unsigned long)msc_win_block(win, i), 1);
-#endif
+	msc_buffer_set_uc(win, ret);
 
 	win->nr_blocks = ret;
 
@@ -860,8 +880,6 @@ static void __msc_buffer_win_free(struct msc *msc, struct msc_window *win)
  */
 static void msc_buffer_win_free(struct msc *msc, struct msc_window *win)
 {
-	int i;
-
 	msc->nr_pages -= win->nr_blocks;
 
 	list_del(&win->entry);
@@ -870,11 +888,7 @@ static void msc_buffer_win_free(struct msc *msc, struct msc_window *win)
 		msc->base_addr = 0;
 	}
 
-#ifdef CONFIG_X86
-	for (i = 0; i < win->nr_blocks; i++)
-		/* Reset the page to write-back */
-		set_memory_wb((unsigned long)msc_win_block(win, i), 1);
-#endif
+	msc_buffer_set_wb(win);
 
 	__msc_buffer_win_free(msc, win);