[PowerPC] Remove extra instruction left by emitRLDICWhenLoweringJumpTables

The function emitRLDICWhenLoweringJumpTables in PPCMIPeephole.cpp
was supposed to convert a pair of RLDICL and RLDICR to a single RLDIC,
but it was leaving out the RLDICL instruction. This PR fixes the bug.

Differential Revision: https://reviews.llvm.org/D78063