fsl-i2c: fix writes to data segment before relocation

Prevent i2c_init() in fsl_i2c.c from writing to the data segment before
relocation.  Commit d8c82db4 added the ability for i2c_init() to program the
I2C bus speed and save the value in i2c_bus_speed[], which is a global
variable.  It is an error to write to the data segment before relocation,
which is what i2c_init() does when it stores the bus speed in i2c_bus_speed[].

Signed-off-by: Timur Tabi <timur@freescale.com>