drm/amd: fix improper docstring syntax

This fixes various warnings relating to erroneous docstring syntax, of
which some are listed below:

 warning: Function parameter or member 'adev' not described in
 'amdgpu_atomfirmware_ras_rom_addr'
 ...
 warning: expecting prototype for amdgpu_atpx_validate_functions().
 Prototype was for amdgpu_atpx_validate() instead
 ...
 warning: Excess function parameter 'mem' description in 'amdgpu_preempt_mgr_new'
 ...
 warning: Cannot understand  * @kfd_get_cu_occupancy - Collect number of
 waves in-flight on this device
 ...
 warning: This comment starts with '/**', but isn't a kernel-doc
 comment. Refer Documentation/doc-guide/kernel-doc.rst

Signed-off-by: Isabella Basso <isabbasso@riseup.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>