staging: iio: resolver: fix comparison to NULL

Remove comparison of spi->dev.platform_data to NULL by replacing it with
'!spi->dev.platform_data' as checkpatch suggested:

CHECK: Comparison to NULL could be written "!spi->dev.platform_data"
Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/resolver/ad2s1210.c

@@ -675,7 +675,7 @@ static int ad2s1210_probe(struct spi_device *spi)
 	struct ad2s1210_state *st;
 	int ret;
 
-	if (spi->dev.platform_data == NULL)
+	if (!spi->dev.platform_data)
 		return -EINVAL;
 
 	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));