i2c: deblock i2c bus also if accessed before realocation

If we switch to a different i2c bus in changing the mux config for the
i2c mux, we have to be sure to deblock the bus also before realocation.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
cc: Heiko Schocher <hs@denx.de>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>