[WATCHDOG] struct file_operations should be const

Fix following warnings:
WARNING: struct file_operations should normally be const

Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/watchdog/hpwdt.c b/drivers/watchdog/hpwdt.c
index dad4fe6..7cf32ad 100644
--- a/drivers/watchdog/hpwdt.c
+++ b/drivers/watchdog/hpwdt.c
@@ -602,7 +602,7 @@
 /*
  *	Kernel interfaces
  */
-static struct file_operations hpwdt_fops = {
+static const struct file_operations hpwdt_fops = {
 	.owner = THIS_MODULE,
 	.llseek = no_llseek,
 	.write = hpwdt_write,