cmd/eeprom.c: prepend 0x to hex numbers in output message format

If the numbers do not happen to contain any digits from [a-f], it's
not clear that they are base 16.

Signed-off-by: Klaus H. Sorensen <khso@prevas.dk>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>