MIPS: Use $a0 instead $zero for passing faulting address

Also replaced register numbers with register names to prevent
future similar errors.

This fixes following tests for MIPS32 and MIPS64:
  * 034-call-null
  * 038-inner-null
  * 046-reflect
  * 083-compiler-regressions
  * 123-compiler-regressions-mt
  * 800-smali

Change-Id: I6e49cec60a9c2b0553d7e94c24553e307b70c603