iio: mxs-lradc: remove unneeded mach header inclusion

Headers <mach/mxs.h> and <mach/common.h> are not used in the driver
at all.  Removed the inclusions.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Jonathan Cameron <jic23@kernel.org>