uboot-imx

i2c, core: optimze i2c_set_bus_num()

check first, if we are on the bus, we want to enable. If so,
return immediately, do not calc max adapter number, nor check
other things.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>