drm/amdgpu/userq: update the vm task info during signal ioctl

drm/amdgpu/userq: update the vm task info during signal ioctl

Pagefaults does not have process information correctly populated
as vm->task is not set during vm_init but should be updated while
real submission. So setting that up during signal_ioctl to get
the correct submission process details.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>