v4l: fwnode: Remove now-redundant loop from v4l2_fwnode_parse_reference()

v4l2_fwnode_parse_reference() relied on counting the number of references
for async array memory allocation. The array is long gone so remove
counting the references now.

This also changes how the function arrives in different unsuccessful
return values but the functionality remains unchanged.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>