HID: Drop NULL test on list_entry result

list_entry, which is an alias for container_of, cannot return NULL, as
there is no way to add a NULL value to a doubly linked list.

A simplified version of the semantic match that findds this problem is as
follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@r@
expression x,E;
statement S1,S2;
position p,p1;
@@

*x = list_entry@p(...)
... when != x = E
*if@p1 (x == NULL) S1 else S2
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-lgff.c

@@ -151,11 +151,6 @@ int lgff_init(struct hid_device* hid)
 
 	/* Check that the report looks ok */
 	report = list_entry(report_list->next, struct hid_report, list);
-	if (!report) {
-		err_hid("NULL output report");
-		return -1;
-	}
-
 	field = report->field[0];
 	if (!field) {
 		err_hid("NULL field");