staging: dgap: Remove useless cast on NULL

Cast on NULL to a pointer type is not required. This
patch removes NULL casted to some pointer type.

The sematic patch used is:
@r@
type T;
@@
- (T *)NULL
+ NULL

Build tested it.

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgap/dgap.c

@@ -7028,7 +7028,7 @@ static char *dgap_sindex(char *string, char *group)
 	char *ptr;
 
 	if (!string || !group)
-		return (char *) NULL;
+		return NULL;
 
 	if (*group == '^') {
 		group++;
@@ -7049,7 +7049,7 @@ static char *dgap_sindex(char *string, char *group)
 		}
 	}
 
-	return (char *) NULL;
+	return NULL;
 }
 
 /*