pwm: sl28cpld: Set driver data before registering the PWM chip

It is good practice to set the driver data before registering a device
with a subsystem because the subsystem or the driver core may call back
into the driver implementation. This is not currently an issue, but to
prevent future changes from causing this to break unexpectedly, make
sure that the driver data is set before the PWM chip registration.

Signed-off-by: Thierry Reding <thierry.reding@gmail.com>