ion: check return value from remap_pfn_range

Check the return value of remap_pfn_range and return an error if
it fails.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>