pwm: atmel-hlcdc: Use consistent variable naming

In PWM drivers the variable name "chip" is usually only used for struct
pwm_chip pointers. This driver however used "chip" for its driver data
and pwm_chip pointers are named "chip", too, when there is no driver
data around and "c" otherwise. Instead use "atmel" for driver data and
always "chip" for pwm_chips.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
[thierry.reding@gmail.com: replace ddata by atmel]
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>