MIPS: make thread_saved_pc static

The only user of thread_saved_pc() in non-arch-specific code was removed
in commit 8243d559 ("sched/core: Remove pointless printout in
sched_show_task()"), so it no longer needs to be globally defined for
MIPS and can be made static.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/17303/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>