MIPS: oprofile: Fix backtrace on 64-bit kernel

Fix incorrect cast that always results in wrong address for the new
frame on 64-bit kernels.

Signed-off-by: Aaro Koskinen <aaro.koskinen@nsn.com>
Cc: stable@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8110/


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