aarch64: Fix build error in aarch64_register_move_cost

        * config/aarch64/aarch64.c (aarch64_register_move_cost): Pass a mode
        to GET_MODE_SIZE, not a reg_class_t.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@209517 138bc75d-0d04-0410-961f-82ee72b054a4