Tweaking the irq pattern regex for wakeup reasons

Fixing to match only at the start of the line, so that invalid reasons
like "adb1 adb2" or negative ids don't get matched.

Also, removing a spurious newline introduced in the previous change.

Test: atest FrameworksServicesTests:CpuWakeupStatsTest

Bug: 195684213
Change-Id: Iab70f1a665a71a846a0bf8c186942f96b7e7ae95