fs: unlock the superblock during iterate_supers_type

This function takes super_lock in shared mode, so it should release the
same lock.

Cc: stable@vger.kernel.org # v6.16-rc1
Fixes: af7551cf ("super: remove pointless s_root checks")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Link: https://lore.kernel.org/20250611164044.GF6138@frogsfrogsfrogs


Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>