[MIPS] Fix cpu_mips_translate_address return value

The cleanups in a2c14f947951612b45024095afd2210aa7368773 fixed a bug
in the error handling path of do_translate_address(). In turn this
exposed a bug in cpu_mips_translate_address() which was always
returning an error that do_translate_address() had ignored.

The cleanup change to do_translate_address() was reverted in
28a24c94e7350a80d5e7e186289cde6a1300bdfb, but fixing
cpu_mips_translate_address() is the correct thing to do.

Change-Id: I442d71130b758fdbe8e864dcba0ba3141b0fe225
2 files changed