ANDROID: binder: fix up use of MAX_USER_RT_PRIO

Commit e00eb41c ("ANDROID: binder: add support for RT prio
inheritance.") added the use of MAX_USER_RT_PRIO to the binder.c code,
but that commit was never sent upstream.

In commit ae18ad28 ("sched: Remove MAX_USER_RT_PRIO"), that define
was taken away, so to fix up the build breakage, move the binder code to
use MAX_RT_PRIO instead of the now-removed MAX_USER_RT_PRIO define.

Hopefully this is correct, who knows, it's binder RT code!  :)

Bug: 34461621
Bug: 37293077
Bug: 120446518
Fixes: e00eb41c ("ANDROID: binder: add support for RT prio inheritance.")
Fixes: ae18ad28 ("sched: Remove MAX_USER_RT_PRIO")
Cc: Martijn Coenen <maco@google.com>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Alistair Strachan <astrachan@google.com>
Cc: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I66b85e99697fdde462ec2d2ade5c92d5917896a3