hw/drivers/pwm: Fix error code return on open/close pwm_nrf52
hw/drivers/pwm: Fix error code return on open/close pwm_nrf52

Be consistent and return OS_ERR in os_dev_open and os_dev_close
functions

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core