Adapted to new name of ioremap_cached function

Recently the function previously called ioremap_cached was renamed to
only ioremap_cache. Adjusting this solves a build error on recent kernel
versions.

The name change was done in commit:
  0a5ccc86507f45b80831dac1049197c4d45be955
in the Linux kernel in the middle of 3.13.0.

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>