I2C: Fix mxc_i2c.c problem on imx31_phycore

I2C: Fix mxc_i2c.c problem on imx31_phycore

The problem was caused by a global variable being used early in the boot
process.

The symptoms were on imx31_phycore board, reading the environment from I2C
EEPROM didn't work correctly and causes default environment to be loaded.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Cc: Heiko Schocher <hs@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Acked-by: Heiko Schocher <hs@denx.de>
Tested-by: Anatolij Gustschin <agust@denx.de>
Tested-by: Stefano Babic <sbabic@denx.de>