Hi,

As per my understanding please try these things 

1)locate where the Go source files are installed on your system, maybe in $GOROOT/src directory.
2)You may need to include this to your sdk to ensure it is added.

May need to add this line to, your recipe
FILES:${PN}-dev += "${datadir}/go/src"

Then try to rebuild your SDK.

Thanks & Regards

Brati