Use typedef names in api.rst for Doxygen

[kaol]

resolves #___

Summary of proposed changes:

• Use typedef names instead of struct/enum names in api.rst for Doxygen

Since Doxyfile declares TYPEDEF_HIDES_STRUCT = YES the documentation needs to use typedef names instead of struct/enum names. This fixes the warnings like

doxygenenum: Cannot find enum “hipfftType_t” in doxygen xml output for project “hipFFT 1.0.14 Documentation” from directory: /home/docs/checkouts/readthedocs.org/user_builds/advanced-micro-devices-hipfft/checkouts/latest/docs/doxygen/xml

as visible with the current version of https://rocm.docs.amd.com/projects/hipFFT/en/latest/api.html.