drm/amd/amdgpu/smuio_v13_0: Realign 'smuio_v13_0_is_host_gpu_xgmi_supported()' header

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/smuio_v13_0.c:99: warning: expecting prototype for smuio_v13_0_supports_host_gpu_xgmi(). Prototype was for smuio_v13_0_is_host_gpu_xgmi_supported() instead

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>