clk_disable_unprepare() is missed on failure paths in ocores_i2c_probe().

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>