ANDROID: uid_sys_stats: report uid_cputime stats in microseconds

A porting error in commit e722dfcb ("ANDROID: uid_cputime: fix
cputime overflow") caused /proc/uid_cputime/show_uid_stat to report
times in milliseconds instead of microseconds. Restore the expected
behavior.

Bug: 133273154
Test: cat /proc/uid_cputime/show_uidstat and check times are in us
Change-Id: I9c666d858edb64a92269f1b6659ee78a91fc6a54
Signed-off-by: Connor O'Brien <connoro@google.com>