xfs: fold __xlog_state_release_iclog into xlog_state_release_iclog

Fold __xlog_state_release_iclog into its only caller to prepare
make an upcoming fix easier.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>