msm: lpm-levels: Remove incorrect BUG_ON() called from hotplug path

The cluster_select() code is used for hotplug as well. When cores are
hotplugged as a result of suspend/resume, the cores in the cluster would
be offline, resulting in the cpumask_and() evaluating to 0, resulting
in the control hitting the incorrect BUG_ON().

Change-Id: Ifa4d7e1ee06384a2e371663294bfbe68bb4d523a
Signed-off-by: Praveen Chidambaram <pchidamb@codeaurora.org>