backlight: pwm_bl: Add missing curly branches in else branch

Add curly braces to an 'else' branch in pwm_backlight_update_status()
to match the corresponding 'if' branch.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>