Fix (null) problem for AVR32 boards

Currently the U-Boot address ranges for AVR32 boards are
printed like this:
"U-Boot code: (null) -> 0001183c  data: 000188e8 -> 0004e9b0"
This patch fixes this to print:
"U-Boot code: 00000000 -> 0001183c  data: 000188f8 -> 0004e9c0"

Signed-off-by: Reinhard Meyer <info@emk-elektronik.de>