The scm device must be present in order for the rmtfs driver to
configure memory permissions for the rmtfs memory region, so check that
it is probed before continuing.

Cc: stable@vger.kernel.org
Fixes: fa65f804 ("soc: qcom: rmtfs-mem: Add support for assigning memory to remote")
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>