fb: change rules for global rules match.

Having a : should be enough 'fb:' isn't really useful
if the fb wants to a kms output ID.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index a85c818..750c71f 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1789,7 +1789,7 @@
  		global = 1;
  	}
 
- 	if (!global && !strstr(options, "fb:")) {
+ 	if (!global && !strchr(options, ':')) {
  		fb_mode_option = options;
  		global = 1;
  	}