[SCSI] qla2xxx: Remove redundant call to pci_unmap_sg().

In a corner-case failure where the request-q does not
contain enough entries for a given request, pci_unmap_sg()
would be called twice.  Remove direct call and let the
failure-path logic handle the unmapping.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>