clk: max77686: Fix clean-up in error and remove paths

This patch fixes invalid kfree() and adds missing call to clk_unregister()
in error and remove paths in max77686_clk_probe(). While at it, error
handling is also cleaned up.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>