i2c: mt7621: fix missing clk_disable_unprepare() on error in mtk_i2c_probe()

Fix the missing clk_disable_unprepare() before return
from mtk_i2c_probe() in the error handling case.

Fixes: d04913ec

 ("i2c: mt7621: Add MediaTek MT7621/7628/7688 I2C driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>