drm/amdgpu: double free error and freeing uninitialized null pointer

Fix a double free and an uninitialized pointer read error. Both tmp and
new are pointing at same address and both are freed which leads to
double free. Adding a check to verify if new and tmp are free in the
error_free label fixes the double free issue. new is not initialized to
null which also leads to a free on an uninitialized pointer.

Reviewed-by: André Almeida <andrealmeid@igalia.com>
Suggested by: S. Amaranath <Amaranath.Somalapuram@amd.com>
Signed-off-by: Sebin Sebastian <mailmesebin00@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>