leds: qti-flash: Show on_time and off_time in microseconds

Adjust the units of on_time and off_time to microseconds to align with
max_flash_timeout, which uses those units.

Change-Id: I65f29175606d5571720215f196d2e08e6d6a18f0
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>