ACPI: property: Get rid of redundant 'else'

In the snippets like the following

	if (...)
		return / goto / break / continue ...;
	else
		...

the 'else' is redundant. Get rid of it.

While at it, replace conditional '<= 0' for unsigned type by '== 0'
in acpi_data_prop_read(); update comment in the
__acpi_node_get_property_reference() on how we parse the reference.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>