i2c: uniphier: avoid WARN_ON() of clk_disable() in failure path

If clk_prepare_enable() fails, clk_disable_unprepare() is called in
the failure path, where the enable_count is still zero, so it hits
WARN_ON(core->enable_count == 0) in the clk_core_disable().

To fix this, make the clock setting more linear in the probe function
so that it can exploit "goto err" in case of error.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>