Scons: Helper: fix size output for avr
Scons: Helper: fix size output for avr

With our changes to the build system avr now has
a DEVICE_FILE env variable, too.

dergraaf/xpcc,chrism333/xpcc,dergraaf/xpcc,chrism333/xpcc,chrism333/xpcc,dergraaf/xpcc,dergraaf/xpcc,chrism333/xpcc