target/mips: Pass a valid error to raise_mmu_exception for user-only

target/mips: Pass a valid error to raise_mmu_exception for user-only

At present we give ret = 0, or TLBRET_MATCH.  This gets matched
by the default case, which falls through to TLBRET_BADADDR.
However, it makes more sense to use a proper value.  All of the
tlb-related exceptions are handled identically in cpu_loop.c,
so TLBRET_BADADDR is as good as any other.  Retain it.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>