scsi: qla2xxx: Fix SRB allocation flag to avoid sleeping in IRQ context

This patch fixes SRB allocation flag from GFP_KERNEL to GFP_ATOMIC, to
prevent sleeping in IRQ context

Signed-off-by: Giridhar Malavali <gmalavali@marvell.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>