[LinuxCNC/linuxcnc PR#331] all: update FSF address in GPL 2.0 notices

If you write to 59 Temple Place you’re unlikely to get a response.
Let’s realign the address with a more up-to-date one from [1].

[1] https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

This is purely a cosmetic change, doesn’t affect the meaning of the
license. Done to make rpmlint happy.

Signed-off-by: Lubomir Rintel