[SCSI] libsas: Fix various sparse complaints

Annotate sas_queuecommand with locking details, and clean up a few
more sparse warnings about static/non-static declarations.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>