iio: health: max30102: Fix mode config values

Table 4 of the datasheet specifies the mode control, these are not
individual bits; add multi LED mode

Add multi-LED mode and fix MODE_MASK (3 bits wide, not 2)

Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>