ANDROID: binder: fix integer as NULL assignment

Fixes the following sparse warning:

  drivers/android/binder_alloc.c:883:25: warning: Using plain integer as NULL pointer

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401190625.6EvaSCpr-lkp@intel.com/


Fixes: 63f7ddea ("ANDROID: binder: fix KMI-break due to address type change")
Change-Id: I1ac36c879c3396c1c4945602c1dfdc6e3b192b47
Signed-off-by: Carlos Llamas <cmllamas@google.com>