staging: ion: msm: Apply d82ad70e to msm_ion_custom_ioctl

Commit d82ad70e ("staging: android: ion: fix ION_IOC_{MAP,SHARE}
use-after-free") removed the definition of ion_handle_get_by_id,
replacing it with a lockless version. Update msm_ion_custom_ioctl with
this same definition and scheme.

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>