mmc: sdhci-pxav2: switch to managed clk and sdhci_pltfm_unregister()

The difference between sdhci_pxav2_remove() and sdhci_pltfm_unregister()
is clk_put().  It will go away by using the managed resource clk, then
sdhci_pltfm_unregister() can be reused.

Also, rename the jump labels to say what the goto does. (Coding style
suggested by Documentation/process/coding-style.rst)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>