btrfs: convert pr_* to btrfs_* where possible

For many printks, we want to know which file system issued the message.

This patch converts most pr_* calls to use the btrfs_* versions instead.
In some cases, this means adding plumbing to allow call sites access to
an fs_info pointer.

fs/btrfs/check-integrity.c is left alone for another day.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3395,7 +3395,7 @@ do {								\
 __cold
 static inline void assfail(char *expr, char *file, int line)
 {
-	pr_err("BTRFS: assertion failed: %s, file: %s, line: %d",
+	pr_err("assertion failed: %s, file: %s, line: %d\n",
 	       expr, file, line);
 	BUG();
 }