fixes incorrect calculation of input length of rocfft r2c type

[hoptony]

fixes 2D && 3D incorrect calculation of input length of rocfft real2complex type

[psteinb]

@hoptony thanks for this contribution. Maybe @tdd11235813 or @zyzzyxdonta can comment too?

[zyzzyxdonta]

I haven't used rocfft, sorry 🤷‍♂️

[zyzzyxdonta]

I wanted to try it out but quickly failed because I can't get rocm and rocfft to build on my machine.

However, I noticed that gearshifft's build system is broken with CMake >= 3.17 because it uses a variable name starting with CMAKE (CMAKE_DEFAULT_BUILD_TYPE) and that name was introduced in CMake 3.17 to actually mean something. Maybe it could be renamed using the GEARSHIFFT_ prefix:

sed -i 's/CMAKE_DEFAULT_BUILD_TYPE/GEARSHIFFT_DEFAULT_BUILD_TYPE/g' cmake/init_build_type.cmake

@hoptony I noticed you commented out the old code and left it in. Maybe you could remove it. This would decrease the number of changed lines in your PR dramatically and the change would be more easily understandable by looking at the diff.