driver core: platform: Make platform_get_irq_optional() optional

Currently the platform_get_irq_optional() returns an error code even
if IRQ resource sumply has not been found. It prevents caller to be
error code agnostic in their error handling.

Now:
	ret = platform_get_irq_optional(...);
	if (ret != -ENXIO)
		return ret; // respect deferred probe
	if (ret > 0)
		...we get an IRQ...

After proposed change:
	ret = platform_get_irq_optional(...);
	if (ret < 0)
		return ret;
	if (ret > 0)
		...we get an IRQ...

Reported-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210331144526.19439-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>