platform/chrome: cros_ec_proto: drop BUG_ON() in cros_ec_get_host_event()

It is overkill to crash the kernel if the `ec_dev` doesn't support MKBP
event but gets called into cros_ec_get_host_event().

Drop the BUG_ON() and return error (0 in the case) instead.

Reviewed-by: Guenter Roeck <[e-mail]>
Signed-off-by: Tzung-Bi Shih <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/platform/chrome/cros_ec_proto.c

···
 {
 	u32 host_event;
 
-	BUG_ON(!ec_dev->mkbp_event_supported);
+	if (!ec_dev->mkbp_event_supported)
+		return 0;
 
 	if (ec_dev->event_data.event_type != EC_MKBP_EVENT_HOST_EVENT)
 		return 0;