iio: kfifo: mask flags without zero-check in devm_iio_kfifo_buffer_setup()

As pointed by Lars, this doesn't require a zero-check. Also, while looking
at this a little closer at it (again), the masking can be done later, as
there is a zero-check for 'mode_flags' anyway, which returns -EINVAL. And
we only need the 'mode_flags' later in the logic.

This change is more of a tweak.

Fixes: e36db6a0 ("iio: kfifo: add devm_iio_kfifo_buffer_setup() helper")
Cc: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210306162834.7339-1-ardeleanalex@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/buffer/kfifo_buf.c

@@ -225,9 +225,6 @@ int devm_iio_kfifo_buffer_setup(struct device *dev,
 {
 	struct iio_buffer *buffer;
 
-	if (mode_flags)
-		mode_flags &= kfifo_access_funcs.modes;
-
 	if (!mode_flags)
 		return -EINVAL;
 
@@ -235,6 +232,8 @@ int devm_iio_kfifo_buffer_setup(struct device *dev,
 	if (!buffer)
 		return -ENOMEM;
 
+	mode_flags &= kfifo_access_funcs.modes;
+
 	indio_dev->modes |= mode_flags;
 	indio_dev->setup_ops = setup_ops;