drivers: qcom: rpmh-rsc: return if the controller is idle

Allow the controller status be queried. The controller is busy if it is
actively processing request.

Change-Id: Id05d27b19dce0a6fbc0946e9857141933997b31c
Signed-off-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>