ANDROID: fix use of plain integer as NULL pointer

This patch fixes the following sparse issues:

  drivers/android/binder.c:1373:70: sparse: sparse: Using plain integer as NULL pointer
  drivers/android/binder.c:2508:41: sparse: sparse: Using plain integer as NULL pointer

Fixes: e107ea9e ("ANDROID: vendor_hooks: Add hooks for binder proc transaction")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304150607.IuUhkfxB-lkp@intel.com/


Cc: zhengding chen <chenzhengding@oppo.com>
Change-Id: I272b3239e2d81bfdd28d1fe412f2c3d0731ec50f
Signed-off-by: Carlos Llamas <cmllamas@google.com>