drm/amdkfd: Use memdup_user() rather than duplicating its implementation

To prevent its redundant implementation and streamline
code, use memdup_user.

This fixes warnings reported by Coccinelle:
./drivers/gpu/drm/amd/amdkfd/kfd_device_queue_manager.c:2811:13-20: WARNING opportunity for memdup_user

Signed-off-by: Atul Raut <rauji.raut@gmail.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>