Allow the current for both RED and IR LEDs to be set via an device tree
property setting.

This is an optional setting that is useful for applications that have a
known glass attenuation factor.

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>