sched: removal of redundant check in Credit

sched: removal of redundant check in Credit

The patch gets rid of a redundant check in csched_vcpu_acct. In fact,
the function is only called from csched_tick, which already checks
that current is not the idle vcpu. The patch also adds an ASSERT to
the same effect, in order to make assumption ( i.e., no calling this
on idle vcpus) even more clear and as a guard for future mis-use.

Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
Acked-by: Dario Faggioli <dario.faggioli@citrix.com>