cmake: fix detection when openmp is enabled

[stkw0]

When openmp was enabled it was falling with the next error:

CMake Error at /usr/lib64/cmake/kissfft/kissfft-config.cmake:104 (message):
  kissfft with datatype=simd is not installed
Call Stack (most recent call first):
  CMakeLists.txt:9 (find_package)

because on the last version it was changed to install with "-openmp" suffix if openmp was enabled, but this change was not applied to kissfft-config.cmake.in file.