intel_th: msu: Remove set but not used variable 'last'

Commit aad14ad3 ("intel_th: msu: Add current window tracking") added
the following gcc warning:

> drivers/hwtracing/intel_th/msu.c: In function msc_win_switch:
> drivers/hwtracing/intel_th/msu.c:1389:21: warning: variable last set but
> not used [-Wunused-but-set-variable]

Fix it by removing the variable.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Fixes: aad14ad3 ("intel_th: msu: Add current window tracking")
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/20190621161930.60785-3-alexander.shishkin@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/intel_th/msu.c

@@ -1400,10 +1400,9 @@ static int intel_th_msc_init(struct msc *msc)
 
 static void msc_win_switch(struct msc *msc)
 {
-	struct msc_window *last, *first;
+	struct msc_window *first;
 
 	first = list_first_entry(&msc->win_list, struct msc_window, entry);
-	last = list_last_entry(&msc->win_list, struct msc_window, entry);
 
 	if (msc_is_last_win(msc->cur_win))
 		msc->cur_win = first;