btrfs: better handle btrfs_printk() defaults

Commit 262c5e86fec7 ("printk/btrfs: handle more message headers")
triggers:

    warning: `ratelimit' may be used uninitialized in this function

with gcc (4.1.2) and probably many other versions.  The code actually is
correct but a bit twisted.  Let's make it more straightforward and set
the default values at the beginning.

Link: http://lkml.kernel.org/r/20161213135246.GQ3506@pathway.suse.cz
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/super.c

@@ -202,12 +202,12 @@ static struct ratelimit_state printk_limits[] = {
 void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 {
 	struct super_block *sb = fs_info->sb;
-	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1];
+	char lvl[PRINTK_MAX_SINGLE_HEADER_LEN + 1] = "\0";
 	struct va_format vaf;
 	va_list args;
-	const char *type = NULL;
 	int kern_level;
-	struct ratelimit_state *ratelimit;
+	const char *type = logtypes[4];
+	struct ratelimit_state *ratelimit = &printk_limits[4];
 
 	va_start(args, fmt);
 
@@ -223,12 +223,6 @@ void btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt, ...)
 		fmt += size;
 	}
 
-	if (!type) {
-		*lvl = '\0';
-		type = logtypes[4];
-		ratelimit = &printk_limits[4];
-	}
-
 	vaf.fmt = fmt;
 	vaf.va = &args;