targets/basys3: Change arty to basys3 in  makefile's error string
targets/basys3: Change arty to basys3 in  makefile's error string

mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware