tg3: missing break statement in tg3_get_5720_nvram_info()

There is a missing break statement so FLASH_5762_EEPROM_HD gets treated
like FLASH_5762_EEPROM_LD.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>