net: smc91x: 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
  18709	    401	      0	  19110	   4aa6	drivers/net/ethernet/smsc/smc91x.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  18901	    201	      0	  19102	   4a9e	drivers/net/ethernet/smsc/smc91x.o
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/smsc/smc91x.c

@@ -2485,7 +2485,7 @@ static int smc_drv_resume(struct device *dev)
 	return 0;
 }
 
-static struct dev_pm_ops smc_drv_pm_ops = {
+static const struct dev_pm_ops smc_drv_pm_ops = {
 	.suspend	= smc_drv_suspend,
 	.resume		= smc_drv_resume,
 };