i2c: rockchip: De-initialize the bus after start bit failure

Failure can happen when i2c is used without initializing pinctrl properly,
which U-Boot happily allows in SPL. Without this fix, further I2C access would
fail, even after proper pinctrl initialization.

Signed-off-by: Ondrej Jirman <megi@xff.cz>
Cc: Heiko Schocher <hs@denx.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Heiko Schocher <hs@denx.de>