btrfs: add __KERNEL__ check for btrfs_no_printk

We want to override this in btrfs-progs, so wrap this in the __KERNEL__
check so we can easily sync this to btrfs-progs and have our local
version of btrfs_no_printk do the work.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/messages.h

@@ -7,11 +7,18 @@
 
 struct btrfs_fs_info;
 
+/*
+ * We want to be able to override this in btrfs-progs.
+ */
+#ifdef __KERNEL__
+
 static inline __printf(2, 3) __cold
 void btrfs_no_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 }
 
+#endif
+
 #ifdef CONFIG_PRINTK
 
 #define btrfs_printk(fs_info, fmt, args...)				\