ui: Only set brightness when needed.

There is a regression due to recent change in commit
b76af93a, where it started to set
brightness to normal on every key input. This is unneeded and spamming
the recovery log.

Test: Run recovery_unit_test on marlin.
Test: Built and boot into recovery image. Press a few keys, then check
      the recovery log.
Change-Id: Ia3a7ea400bcccdebbb27a6a7586e435bfb915923