power: bcl: Clear the hotplug mask immediately

When disabling BCL the hotplug mask will be
cleared by a separate work event and hence
it is not immediate. So there is a possibility
that BCL will prevent a core online before
this work event is executed.

Update the BCL disable code path to clear the
hotplug request mask immediately.

CRs-Fixed: 806903
Change-Id: I3cc0e8fc49e3b89b551d79978324ad48282ab05f
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>