Reuse math_brute_force ulp threshold in spir test

Spir test compares floating-point kernel results bit-by-bit with
correct results. However, for math_brute_force kernels, specification
does not ask for SPIR and OpenCL C path to match bit-to-bit. This patch
reuses ulps threshold from math_brute_force folder for math_brute_force
kernels in spir test.

Signed-off-by: Wenju He <wenju.he@intel.com>