Fix vector widths of constants in fast_log and fast_exp
Fix vector widths of constants in fast_log and fast_exp


Former-commit-id: 016c89c0913ad39d40d2c60b4a0b0c1e3541ac75
darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide