USB: EHCI: ehci-mv: improve error handling in mv_ehci_enable()

mv_ehci_enable() did not disable and unprepare clocks in case of
failures of phy_init(). Besides, it did not take into account failures
of ehci_clock_enable() (in effect, failures of clk_prepare_enable()).
The patch fixes both issues and gets rid of redundant wrappers around
clk_prepare_enable() and clk_disable_unprepare() to simplify this a bit.

Found by Linux Driver Verification project (linuxtesting.org).

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Link: https://lore.kernel.org/r/20210708083056.21543-1-novikov@ispras.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>