[LLDB][MIPS] Fix TestDisassembleBreakpoint.py for MIPS

Patch by Nitesh Jain

Summary: The break is opcode for breakpoint instruction.

Subscribers: lldb-commits, mohit.bhakkad, sagar, bhushan
Reviewers: clayborg, ovyalov, jaydeep
Differential: http://reviews.llvm.org/D14634
llvm-svn: 253445