scsi: ibmvscsi: constify dev_pm_ops structures.

dev_pm_ops are not supposed to change at runtime. All functions working
with dev_pm_ops provided by <linux/device.h> work with const
dev_pm_ops. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
  17956	   1456	      8	  19420	   4bdc	drivers/scsi/ibmvscsi/ibmvscsi.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  18164	   1264	      8	  19436	   4bec	drivers/scsi/ibmvscsi/ibmvscsi.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Acked-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>