POST_SGL_PAGES mailbox command failed with status (timeout).

wait_event_interruptible_timeout when called from mailbox wait interface,
gets interrupted, and will randomly fail. Behavior seems very specific to 1
particular server type.

Fix by changing from wait_event_interruptible_timeout to
wait_for_completion_timeout.
Signed-off-by: NDick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: NJames Smart <james.smart@broadcom.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>