drm/amd/amdgpu/amdgpu_ids: Correct some function name disparity

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

 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:200: warning: expecting prototype for amdgpu_vm_grab_idle(). Prototype was for amdgpu_vmid_grab_idle() instead
 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:272: warning: expecting prototype for amdgpu_vm_grab_reserved(). Prototype was for amdgpu_vmid_grab_reserved() instead
 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:337: warning: expecting prototype for amdgpu_vm_grab_used(). Prototype was for amdgpu_vmid_grab_used() instead
 drivers/gpu/drm/amd/amdgpu/amdgpu_ids.c:410: warning: expecting prototype for amdgpu_vm_grab_id(). Prototype was for amdgpu_vmid_grab() 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: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>