samples: led: pwm: fix console harness regex

Led blinking period was made configurable and time unit changed
from sec to msec recently in the source code of the sample.
Console harness regex was not changed accordingly in sample.yaml.
Device testing fails when run with twister.
Change the regex to accept any period and change the units to msec.

Signed-off-by: Michal Smola <michal.smola@nxp.com>