ANDROID: binder: fix regression in sender_euid

A recent change to use proc->cred instead of proc->tsk as the source
for sender_euid caused a failure in the CredentialsTest#CaptureLayersTest
test. Revert 1 line of the patch to fix the test. The rest of the patch
needs to remain since the subsequent patches rely on it.

Before fixing upstream, we need to investigate more since the code looks
correct so the issue may be a latent userspace bug.

Bug: 205938623
Fixes: d65efd5b ("UPSTREAM: binder: use euid from cred instead of using task")
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: I16543a50f43f79131234995fb0813de00795bd3d