pwm-backlight: take over maintenance

Since the pwm-backlight driver is lacking a proper maintainer and is the
heaviest user of the PWM framework I'm taking over maintenance.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Arun Murthy <arun.murthy@stericsson.com>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: Robert Morell <rmorell@nvidia.com>
Cc: Dilan Lee <dilee@nvidia.com>
Cc: Axel Lin <axel.lin@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>