i2c: xlr: Fix a resource leak in the error handling path of 'xlr_i2c_probe()'

A successful 'clk_prepare()' call should be balanced by a corresponding
'clk_unprepare()' call in the error handling path of the probe, as already
done in the remove function.

More specifically, 'clk_prepare_enable()' is used, but 'clk_disable()' is
also already called. So just the unprepare step has still to be done.

Update the error handling path accordingly.

Fixes: 75d31c23

 ("i2c: xlr: add support for Sigma Designs controller variant")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Wolfram Sang <wsa@kernel.org>