iio: adc: mxs-lradc: fix warning when buidling on avr32

This fixes:
drivers/staging/iio/adc/mxs-lradc.c: In function 'mxs_lradc_probe':
drivers/staging/iio/adc/mxs-lradc.c:1558: warning: comparison of distinct pointer types lacks a cast
drivers/staging/iio/adc/mxs-lradc.c:1558: warning: right shift count >= width of type
drivers/staging/iio/adc/mxs-lradc.c:1558: warning: passing argument 1 of '__div64_32' from incompatible pointer type

When building on avr32.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>