[Matrix] Only pass vector arg as overloaded type in MatrixBuilder.

In 2b3c505d, the pointer arguments for the matrix load and store
intrinsics was changed to always be the element type of the vector
argument.

This patch updates the MatrixBuilder to not add the pointer type to the
overloaded types and adjusts the clang/mlir tests.

This should fix a few build failures on GreenDragon, including
 http://green.lab.llvm.org/green/job/test-suite-verify-machineinstrs-x86_64-O0-g/7891/