Update internal heading link

[saeedjohar]

Corrected a typo in the documentation which seems to be mismatch

[lurch]

Yes, it probably makes more sense to link to the higher-level https://www.raspberrypi.com/documentation/computers/linux_kernel.html#cross-compile-the-kernel section, than it does the lower-level https://www.raspberrypi.com/documentation/computers/linux_kernel.html#cross-compiled-build section.