kernel/sched: Fix up 4.9.135 merge

Commit aee0c9e8 ("sched/cputime: Fix ksoftirqd cputime accounting
regression") moved the calls to u64_stats_update_{begin,end} from
irqtime_account_irq into irqtime_account_delta. This was missed in
commit 03fcc2fe ("Merge 4.9.135 into android-4.9"), which only
removed the u64_stats_update_begin call in irqtime_account_irq, because
of a conflict with commit 3a73c96a ("ANDROID: sched/walt: Accounting
for number of irqs pending on each core").

Since the two code blocks above and below this statement were gated by
CONFIG_SCHED_WALT, combine them into one at the same time.

Change-Id: I25e9e5a2f063f8df53fa4ff2cfc26dced6ec2b02
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>