[SCSI] zfcp: Fix request queue locking

The request queue lock can be acquired from softirq context when the
SCSI midlayer issues commands. Disable softirqs for this lock when
commands are issued from zfcp.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Martin Petermann <martin@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>