pwm: raspberrypi-poe: Fix endianness in firmware struct

The reg member of struct raspberrypi_pwm_prop is a little endian 32 bit
quantity. Explicitly convert the (native endian) value to little endian
on assignment as is already done in raspberrypi_pwm_set_property().

This fixes the following sparse warning:

	drivers/pwm/pwm-raspberrypi-poe.c:69:24: warning: incorrect type in initializer (different base types)
	drivers/pwm/pwm-raspberrypi-poe.c:69:24:    expected restricted __le32 [usertype] reg
	drivers/pwm/pwm-raspberrypi-poe.c:69:24:    got unsigned int [usertype] reg

Fixes: 79caa362 ("pwm: Add Raspberry Pi Firmware based PWM bus")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>