counter: interrupt-cnt: Implement watch_validate callback

The interrupt-cnt counter driver only pushes one type of event on only
one channel: COUNTER_EVENT_CHANGE_OF_STATE on channel 0. The
interrupt_cnt_watch_validate() watch_valid callback is implemented to
ensure watch configurations are valid for this driver.

Cc: Oleksij Rempel <[e-mail]>
Cc: Pengutronix Kernel Team <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]/
Signed-off-by: William Breathitt Gray <[e-mail]>
Link: https://lore.kernel.org/r/c50b[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/counter/interrupt-cnt.c

···
 	return 0;
 }
 
+static int interrupt_cnt_watch_validate(struct counter_device *counter,
+					const struct counter_watch *watch)
+{
+	if (watch->channel != 0 ||
+	    watch->event != COUNTER_EVENT_CHANGE_OF_STATE)
+		return -EINVAL;
+
+	return 0;
+}
+
 static const struct counter_ops interrupt_cnt_ops = {
 	.action_read = interrupt_cnt_action_read,
 	.count_read = interrupt_cnt_read,
 	.count_write = interrupt_cnt_write,
 	.function_read = interrupt_cnt_function_read,
 	.signal_read  = interrupt_cnt_signal_read,
+	.watch_validate  = interrupt_cnt_watch_validate,
 };
 
 static int interrupt_cnt_probe(struct platform_device *pdev)