clk: sunxi: improve divider_clk error handling and reporting

We now report a failing ioremap, failing output names parsing,
failures in table registration and in the final step.
Also there was a bug where clk_register_divider_table() would return
an ERR_PTR value instead of NULL, which we were checking for.
We now implement proper rollback in case of an error.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>