watchdog: bcm47xx_wdt: constify bcm47xx_wdt_hard_ops and bcm47xx_wdt_soft_ops

File size before:
   text	   data	    bss	    dec	    hex	filename
   1282	    388	      1	   1671	    687	drivers/watchdog/bcm47xx_wdt.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   1474	    196	      1	   1671	    687	drivers/watchdog/bcm47xx_wdt.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>