iio: adc: xilinx: use helper variable for &pdev->dev

[ Upstream commit 9d8fd2a0

 ]

It's more elegant to use a helper local variable to store the address
of the underlying struct device than to dereference pdev everywhere.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Tested-by: Anand Ashok Dumbre <anandash@xilinx.com>
Reviewed-by: Anand Ashok Dumbre <anandash@xilinx.com>
Link: https://lore.kernel.org/r/20201130142759.28216-2-brgl@bgdev.pl
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Stable-dep-of: 8d6b3ea4

 ("iio: adc: xilinx-xadc: Don't clobber preset voltage/temperature thresholds")
Signed-off-by: Sasha Levin <sashal@kernel.org>