When configuring FPS during probe, assuming a DT node is present for
FPS, the code can run into a problem with the switch statements in
max77620_config_fps() and max77620_get_fps_period_reg_value(). Namely,
in the case of chip->chip_id == MAX77620, it will set
fps_[mix|max]_period but then fall through to the default switch case
and return -EINVAL. Returning this from max77620_config_fps() will
cause probe to fail.