Previously if MipsCpuCaps were called with something other than
dspr2 or msa, the file was closed but still used.

This change assumed the function is only called internally twice:
once for msa and once for dspr2.  If msa is not being detected,
the function assumed dspr2 was being tested and returns dspr2 was
true.

BUG=libyuv:687
TEST=try bots

Change-Id: I80b328eb5ffc7baf5f1ee5a79c16d75c45ff26cc
Reviewed-on: https://chromium-review.googlesource.com/447831Reviewed-by: Frank Barchard <fbarchard@google.com>
Commit-Queue: Frank Barchard <fbarchard@google.com>