platform/x86: wmi: use !p to check for NULL

Other parts of the code use the `!p` idiom to check
for NULL pointers, convert `find_guid_context()` to
do the same.
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20210904175450.156801-19-pobrn@protonmail.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/wmi.c

@@ -141,10 +141,10 @@ static const void *find_guid_context(struct wmi_block *wblock,
 	const struct wmi_device_id *id;
 	guid_t guid_input;
 
-	if (wdriver->id_table == NULL)
+	id = wdriver->id_table;
+	if (!id)
 		return NULL;
 
-	id = wdriver->id_table;
 	while (*id->guid_string) {
 		if (guid_parse(id->guid_string, &guid_input))
 			continue;