HID: explain the signed/unsigned handling in hid_add_field()

Put a comment that clarifies the condition that handles both signed
and unsigned case for logical min/max in hid_add_field().
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -230,6 +230,7 @@ static int hid_add_field(struct hid_parser *parser, unsigned report_type, unsign
 		return -1;
 	}
 
+	/* Handle both signed and unsigned cases properly */
 	if ((parser->global.logical_minimum < 0 &&
 		parser->global.logical_maximum <
 		parser->global.logical_minimum) ||