This fix allows platforms to probe correctly even if the
trigger edge property is missing. The hardware trigger
will no longer be registered in the sybsystem
Preserves backwards compatibility with the support that
was in the driver before the hardware trigger.

https://storage.kernelci.org/mainline/master/v4.14-rc2-255-g74d83ec2b734/arm/sama5_defconfig/lab-free-electrons/boot-at91-sama5d2_xplained.txtSigned-off-by: NEugen Hristev <eugen.hristev@microchip.com>
Fixes: 5e1a1da0 ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>