drm/amdgpu: fix non-ANSI declaration of amdgpu_amdkfd_gfx_*_get_functions()

amdgpu_amdkfd_gfx_7_get_functions and amdgpu_amdkfd_gfx_8_0_get_functions
have no parameters, so use the normal void parameter convention to make
them  match their prototypes in the header file
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>