Fix mips memory reads.
Fix mips memory reads.

Cast the first 32 bit read to an unsigned value to avoid sign extending the
value up to 64 bits.

Change-Id: Ib678f48acf91f382fd5d8bcbf2be7d5803aaf0b8

SyndicateRogue/libunwind,atanasyan/libunwind-android,olibc/libunwind,geekboxzone/lollipop_external_libunwind,atanasyan/libunwind-android,geekboxzone/mmallow_external_libunwind,androidarmv6/android_external_libunwind,atanasyan/libunwind-android,zeldin/platform_external_libunwind,geekboxzone/lollipop_external_libunwind,androidarmv6/android_external_libunwind,frida/libunwind,olibc/libunwind,DroidSim/platform_external_libunwind,android-ia/platform_external_libunwind,SyndicateRogue/libunwind,CyanogenMod/android_external_libunwind,frida/libunwind,android-ia/platform_external_libunwind,CyanogenMod/android_external_libunwind,zeldin/platform_external_libunwind,DroidSim/platform_external_libunwind,geekboxzone/lollipop_external_libunwind,android-ia/platform_external_libunwind,DroidSim/platform_external_libunwind,androidarmv6/android_external_libunwind,maltek/platform_external_libunwind,maltek/platform_external_libunwind,geekboxzone/mmallow_external_libunwind,frida/libunwind,SyndicateRogue/libunwind,CyanogenMod/android_external_libunwind,zeldin/platform_external_libunwind,maltek/platform_external_libunwind,olibc/libunwind,geekboxzone/mmallow_external_libunwind