Fix C89 compile error for cpu detect.  Make mips detection assume DSP if cpuinfo file can not be opened, so that if run in a sandbox, DSP is assumed true, like the arm version.
BUG=303
TESTED=cl /c /TC /Iinclude source/cpu_id.cc
R=tpsiaki@google.com

Review URL: https://webrtc-codereview.appspot.com/10549004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@986 16f28f9a-4ce2-e073-06de-1de4eb20be90