iio: adc: max1027: Fix style

iio: adc: max1027: Fix style

Follow checkpatch.pl's main advices before hacking into the driver, mainly:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
WARNING: Prefer 'unsigned int *' to bare use of 'unsigned *'
CHECK: Comparison to NULL could be written "!foo"
CHECK: Alignment should match open parenthesis

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20210921115408.66711-2-miquel.raynal@bootlin.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>