ion: check return value from remap_pfn_range

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

Change-Id: I206cf95a24607ebe1c80274e3ed15cc7c076d007
Signed-off-by: Colin Cross <ccross@android.com>
Git-commit: 3b8da00c6c5e42af7b532dbf51b2d5007095d844
Git-repo: http://android.googlesource.com/kernel/common/


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>