[GlobalISel] Fix warnings
This patch fixes:
llvm/lib/CodeGen/GlobalISel/CombinerHelperCasts.cpp:167:21: error:
unused variable 'DL' [-Werror,-Wunused-variable]
llvm/lib/CodeGen/GlobalISel/LoadStoreOpt.cpp:320:15: error: unused
variable 'DL' [-Werror,-Wunused-variable]
