USB: octeon2-common: Don't reinitialize the clocks.

The UCTL clock initialization will cause the ehci and ohci blocks to
become inoperable if the clocks are reinitialized.

Check to see if the clocks have already been initialized.

Also use a mutex to protect the clock initialization code so that
there can be no attempt to use the clocks before they are fully
configured.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>