leds: core: Fix brightness setting upon hardware blinking enabled

leds: core: Fix brightness setting upon hardware blinking enabled

Commit 76931edd54f8 ("leds: fix brightness changing when software blinking
is active") changed the semantics of led_set_brightness() which according
to the documentation should disable blinking upon any brightness setting.
Moreover it made it different for soft blink case, where it was possible
to change blink brightness, and for hardware blink case, where setting
any brightness greater than 0 was ignored.

While the change itself is against the documentation claims, it was driven
also by the fact that timer trigger remained active after turning blinking
off. Fixing that would have required major refactoring in the led-core,
led-class, and led-triggers because of cyclic dependencies.

Finally, it has been decided that allowing for brightness change during
blinking is beneficial as it can be accomplished without disturbing
blink rhythm.

The change in brightness setting semantics will not affect existing
LED class drivers that implement blink_set op thanks to the LED_BLINK_SW
flag introduced by this patch. The flag state will be from now on checked
in led_set_brightness() which will allow to distinguish between software
and hardware blink mode. In the latter case the control will be passed
directly to the drivers which apply their semantics on brightness set,
which is disable the blinking in case of most such drivers. New drivers
will apply new semantics and just change the brightness while hardware
blinking is on, if possible.

The issue was smuggled by subsequent LED core improvements, which modified
the code that originally introduced the problem.

Fixes: f1e80c07416a ("leds: core: Add two new LED_BLINK_ flags")
Signed-off-by: Tony Makkiel <tony.makkiel@daqri.com>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>