MIPS: oprofile: Backtrace: don't fail on leaf functions

Continue the backtrace if we cannot find SP adjustment and RA save. In
that case, just assume the current RA. This allows us to get samples of
frequent callers of e.g. GLIBC memset().

Signed-off-by: Aaro Koskinen <aaro.koskinen@nsn.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8109/


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