healthd_mode_charger: unblank the screen only on first frame

Original code is unblank screen for all frames of the first
cycle, unblank is needed only before the first frame of the
first cycle.

Bug: 74771887
Change-Id: I51d8390e359335a0b1cb127b096db1a8b889b169
Signed-off-by: Thierry Strudel <tstrudel@google.com>