The varible uncached  set false, the condition uncached cannot be true.
So remove the dead code, mapping flags will set the flag AMDGPU_VM_MTYPE_UC in else.
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>