btrfs: move btrfs_pinned_by_swapfile prototype into volumes.h

stable inclusion
from stable-v5.10.197
commit cc87d2bb391cf12feb3c79fec86bc3597e08f3ac
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I96Q8P

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cc87d2bb391cf12feb3c79fec86bc3597e08f3ac



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[ Upstream commit c2e79e86 ]

This is defined in volumes.c, move the prototype into volumes.h.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Stable-dep-of: 6bfe3959 ("btrfs: compare the correct fsid/metadata_uuid in btrfs_validate_super")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>