xfs: close the RT and log block devices in xfs_free_buftarg

Closing the block devices logically belongs into xfs_free_buftarg,  So
instead of open coding it in the caller move it there and add a check
for the s_bdev so that the main device isn't close as that's done by the
VFS helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Message-Id: <20230809220545.1308228-6-hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>