drm/amdkfd: Fix -Wstrict-prototypes from amdgpu_amdkfd_gfx_10_0_get_functions()

This patch is for linux-5.4.y only, it has no equivalent change
upstream.

When building x86_64 allmodconfig with tip of tree clang, there is an
instance of -Wstrict-prototypes:

  drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gfx_v10.c:168:59: error: a function declaration without a prototype is deprecated in all versions of C [-Werror,-Wstrict-prototypes]
  struct kfd2kgd_calls *amdgpu_amdkfd_gfx_10_0_get_functions()
                                                            ^
                                                             void
  1 error generated.

amdgpu_amdkfd_gfx_10_0_get_functions() is prototyped properly in
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.h but its definition in
amdgpu_amdkfd_gfx_v10.c does not have the argument types specified,
which causes the warning. GCC does not warn because it permits an
old-style definition if the prototype has the argument types.

This code was eliminated by commit e392c887 ("drm/amdkfd: Use array
to probe kfd2kgd_calls"), which was a part of a larger series that does
not look very suitable for stable. Just fix this one location, as it was
the only instance of this new warning across a variety of builds.

Fixes: 6bdadb20

 ("drm/amdgpu: Add navi10 kfd support for amdgpu (v3)")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>