ion: fix sparse warnings

Fix sparse warnings in ion.

Change-Id: Icbadf2ca53bea20914f608f619568629c178eae3
Signed-off-by: Colin Cross <ccross@android.com>
Git-commit: 6db8a1c0c9817d6ebd61c47110554aa34729e9a7
Git-repo: http://android.googlesource.com/kernel/common/


[mitchelh@codeaurora.org: conflicts since we have page pooling for both
 cached and uncached as well as some gfp flag differences]
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>