USB: pxa2xx_udc: fix misuse of clock enable/disable calls

Fix pxa2xx_udc to balance calls to clk_enable/clk_disable.

[db: remove inline #ifdefs for IXP non-support of <linux/clk.h> calls]

Signed-off-by: Dmitry Baryshkov <dbaryshkov@gmail.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>