Staging: android: Mark local functions in binder.c as static

This fixes the following sparse warnings
drivers/staging/android/binder.c:1703:5: warning: symbol 'binder_thread_write' was not declared. Should it be static?
drivers/staging/android/binder.c:2058:6: warning: symbol 'binder_stat_br' was not declared. Should it be static?

Change-Id: Ib3fadafe30b5ffa3776270574809823e898caac3
Signed-off-by: Bojan Prtvar <prtvar.b@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>