gfxml2dto:fngsystem: switch from fix commit to master

This is the fix for [redacted](https://secogroup.atlassian.net/browse/YT-182).

During investigation of the problem why our fixes do not make it into final FNG System image, it was found that:

• the problem is caused by the f75621da commit "gfxml2dto:fngsystem: Set fixed SRCREV, don't pull the fec hack for nallino", which specifies that particular version of sources should be used instead of master;
• herewith we failed to comprehend this right away, as a resulted binary did not correspond the seco-ne/tools/gfxml2dto@60b9fbcf SRCREV hardocded in recipe. And we still can't explain this - why a different SRCREV (seco-ne/tools/gfxml2dto@0712cc8b) is built all the time instead of 60b9fbcf;
• anyway, both 60b9fbcf and 0712cc8b, which was really built, are outdated and it is safe to switch back to master now. 60b9fbcf was intended to address problems with FEC in FNG System based on dunfell/linux5.10 when a 'local-mac-address' property was missing in the device tree. We successfully checked that this is not needed any more for FNG System based on Yocto kirkstone - the network works fine on nallino with the latest fngsystem, even if this property is not specified.

Verified using the following image from GitLab: https://git.seco.com/seco-ne/yocto/manifest/-/jobs/1102212
The revision of gfxml2dto could be found in manifest file: https://git.seco.com/seco-ne/yocto/manifest/-/jobs/1102212/artifacts/file/build-seconorth-fngsystem-seco-mx6ull/tmp/deploy/images/seco-mx6ull/fngsystem-image-seco-mx6ull-20240624114728.rootfs.manifest

$ grep gfxml2dto fngsystem-image-seco-mx6ull-20240624114728.rootfs.manifest 
gfxml2dto cortexa7t2hf_neon 0.0+194+g1a36d45