drivers/net/eepro100.c: fix GCC 4.6 build warnings

Fix:
eepro100.c: In function 'read_hw_addr':
eepro100.c:926:6: warning: variable 'eeprom' set but not used
[-Wunused-but-set-variable]

Signed-off-by: Wolfgang Denk <wd@denx.de>