btrfs: zoned: fix uninitialized variable warning in btrfs_get_dev_zones

Fix an uninitialized warning we get with -Wmaybe-uninitialized where it
thought zno may have been uninitialized, in both cases it depends on
zinfo->zone_cache but we know the value won't change between checks.

Reported-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/linux-btrfs/af6c527cbd8bdc782e50bd33996ee83acc3a16fb.1671221596.git.josef@toxicpanda.com/
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/zoned.c

@@ -220,7 +220,6 @@ static int btrfs_get_dev_zones(struct btrfs_device *device, u64 pos,
 			       struct blk_zone *zones, unsigned int *nr_zones)
 {
 	struct btrfs_zoned_device_info *zinfo = device->zone_info;
-	u32 zno;
 	int ret;
 
 	if (!*nr_zones)
@@ -235,6 +234,7 @@ static int btrfs_get_dev_zones(struct btrfs_device *device, u64 pos,
 	/* Check cache */
 	if (zinfo->zone_cache) {
 		unsigned int i;
+		u32 zno;
 
 		ASSERT(IS_ALIGNED(pos, zinfo->zone_size));
 		zno = pos >> zinfo->zone_size_shift;
@@ -274,9 +274,12 @@ static int btrfs_get_dev_zones(struct btrfs_device *device, u64 pos,
 		return -EIO;
 
 	/* Populate cache */
-	if (zinfo->zone_cache)
+	if (zinfo->zone_cache) {
+		u32 zno = pos >> zinfo->zone_size_shift;
+
 		memcpy(zinfo->zone_cache + zno, zones,
 		       sizeof(*zinfo->zone_cache) * *nr_zones);
+	}
 
 	return 0;
 }