drm/amdkfd: fix kgd2kfd_device_init() definition conflict error

The patch c670707 drm/amd: Pass drm_device to kfd introduced this issue and
fix the following compiler error.

  CC [M]  drivers/gpu/drm/amd/amdgpu//../powerplay/smumgr/fiji_smumgr.o
drivers/gpu/drm/amd/amdgpu//amdgpu_amdkfd.c:746:6: error: conflicting types for ‘kgd2kfd_device_init’
 bool kgd2kfd_device_init(struct kfd_dev *kfd,
      ^
In file included from drivers/gpu/drm/amd/amdgpu//amdgpu_amdkfd.c:23:0:
drivers/gpu/drm/amd/amdgpu//amdgpu_amdkfd.h:253:6: note: previous declaration of ‘kgd2kfd_device_init’ was here
 bool kgd2kfd_device_init(struct kfd_dev *kfd,
      ^
scripts/Makefile.build:273: recipe for target 'drivers/gpu/drm/amd/amdgpu//amdgpu_amdkfd.o' failed
make[1]: *** [drivers/gpu/drm/amd/amdgpu//amdgpu_amdkfd.o] Error 1

Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>