ASoC: max98373: check for device node before parsing

ASoC: max98373: check for device node before parsing

Below Oops is caused in a system which uses ACPI instead of device node:

of_get_named_gpiod_flags: can't parse 'maxim,reset-gpio' property of node '(null)[0]'
BUG: kernel NULL pointer dereference, address: 0000000000000010

This patch avoids NULL pointer deferencing by adding a check before parsing
and initializes to make reset-gpio pin as invalid.

Signed-off-by: Sathyanarayana Nujella <sathyanarayana.nujella@intel.com>
Signed-off-by: Jairaj Arava <jairaj.arava@intel.com>
Link: https://lore.kernel.org/r/1569702150-11976-1-git-send-email-sathyanarayana.nujella@intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>