[mips] Range check simm9 and fix a bug this revealed.

Summary:
The bug was that microMIPS's [ls]w[lr]e instructions claimed to support a
12-bit offset when it is only 9-bit.

Reviewers: vkalintiris

Subscribers: llvm-commits, dsanders

Differential Revision: http://reviews.llvm.org/D18434

llvm-svn: 265010