SystemZISelLowering - supportedAddressingMode - silence static analyzer dyn_cast<> null dereference warning. NFCI.
SystemZISelLowering - supportedAddressingMode - silence static analyzer dyn_cast<> null dereference warning. NFCI.

The static analyzer is warning about a potential null dereference, but we should be able to use cast<> directly and if not assert will fire for us.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@375430 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm