cups-drv-rastertosag-gdi (cups driver): patch ppd bin paths
The `cups-drv-rastertosag-gdi` CUPS printer driver
package provides a filter executable `rastertosag-gdi`
and two ppd files that reference the filter file.
The commit at hand uses `patchPpdFilesHook` to
replace calls to the filter executable with
absolute paths to increase package purity.