msm: ion: Only return Ion flags in ion_handle_get_flags

Since the ion_buffer.flags field is shared between the actual Ion
flags as well as the Ion heap mask, make sure that we're only
returning flags. The heap_mask bits should be masked off.

Change-Id: Ibdaf0ea374b7b80a036bddd11d19c4bafa173ef6
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>