drm/amdkfd: uninitialized variable in dbgdev_wave_control_set_registers()

At the end of the function we expect "status" to be zero, but it's
either -EINVAL or uninitialized.

Fixes: 788bf83d ('drm/amdkfd: Add wave control operation to debugger')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>