FSL: Fix get_cpu_board_revision() return value.

get_cpu_board_revision() returned board revision based on information stored
in global static struct eeprom. It should instead use one from local struct
board_eeprom, to which the data is actually read from EEPROM. The bug led to
system hang after printing L1 cache information on U-Boot startup. The problem
was observed on MPC8555CDS system and possibly affects other Freescale MPC85xx
boards using CFG_I2C_EEPROM_CCID.

The change has been successfully tested on MPC8555CDS system.

Signed-off-by: Rafal Czubak <rcz@semihalf.com>