ACPI: property: Fix fwnode string properties matching

ACPI: property: Fix fwnode string properties matching

Property matching does not work for ACPI fwnodes if the value of the
given property is not represented as a package in the _DSD package
containing it.  For example, the "compatible" property in the _DSD
below

  Name (_DSD, Package () {
    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
    Package () {
      Package () {"compatible", "ethernet-phy-ieee802.3-c45"}
    }
  })

will not be found by fwnode_property_match_string(), because the ACPI
code handling device properties does not regard the single value as a
"list" in that case.

Namely, fwnode_property_match_string() invoked to match a given
string property value first calls fwnode_property_read_string_array()
with the last two arguments equal to NULL and 0, respectively, in
order to count the items in the value of the given property, with the
assumption that this value may be an array.  For ACPI fwnodes, that
operation is carried out by acpi_node_prop_read() which calls
acpi_data_prop_read() for this purpose.  However, when the return
(val) pointer is NULL, that function only looks for a property whose
value is a package without checking the single-value case at all.

To fix that, make acpi_data_prop_read() check the single-value
case if its return pointer argument is NULL and modify
acpi_data_prop_read_single() handling that case to attempt to
read the value of the property if the return pointer is NULL
and return 1 if that succeeds.

Fixes: 3708184afc77 ("device property: Move FW type specific functionality to FW specific files")
Reported-by: Calvin Johnson <calvin.johnson@oss.nxp.com>
Cc: 4.13+ <stable@vger.kernel.org> # 4.13+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>