CMakeLists with DaisySP fix

[garnetgrimm]

Hey all! Thank you all so much for maintaining so many wonderful open source tools.

I have a project which is built using cmake and has the DaisySP repo as a submodule. I was super excited to try out reverbsc from DaisySP-LGPL. I added the dependency as follows

add_subdirectory(DaisySP)
add_subdirectory(DaisySP/DaisySP-LGPL)

However, I ran into an error when trying to build

ggrimm@fedora:~/Desktop/CCAM-Earth-Init/build$ make
[ 16%] Built target DaisySP
[ 16%] Building CXX object DaisySP/DaisySP-LGPL/CMakeFiles/DaisySP_LGPL.dir/Source/Control/line.cpp.obj
[ 16%] Building CXX object DaisySP/DaisySP-LGPL/CMakeFiles/DaisySP_LGPL.dir/Source/Dynamics/balance.cpp.obj
/home/ggrimm/Desktop/CCAM-Earth-Init/DaisySP/DaisySP-LGPL/Source/Dynamics/balance.cpp:3:10: fatal error: dsp.h: No such file or directory
    3 | #include "dsp.h"

When I looked into it a bit more, it seems like the CmakeLists.txt is reaching too far back, and I was able to fix the issue with the following changes