gpu: host1x: channel: Use correct type

find_first_zero_bit() returns an unsigned long, so make the local
variable that stores the result the same type for consistency.

Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/host1x/channel.c

···
 	struct host1x *host = dev_get_drvdata(dev->parent);
 	unsigned int max_channels = host->info->nb_channels;
 	struct host1x_channel *channel = NULL;
-	int index, err;
+	unsigned long index;
+	int err;
 
 	mutex_lock(&host->chlist_mutex);