usb: replace wait_ms() with mdelay()

Common code has a mdelay() func, so use that instead of the usb-specific
wait_ms() func.  This also fixes the build errors:

ohci-hcd.c: In function 'submit_common_msg':
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1519:9: sorry, unimplemented: called from here
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1816:10: sorry, unimplemented: called from here
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1827:10: sorry, unimplemented: called from here
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1844:10: sorry, unimplemented: called from here
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1563:11: sorry, unimplemented: called from here
/usr/local/src/u-boot/blackfin/include/usb.h:202:44: sorry, unimplemented: inlining failed in call to 'wait_ms': function body not available
ohci-hcd.c:1583:9: sorry, unimplemented: called from here
make[1]: *** [ohci-hcd.o] Error 1

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Marek Vasut <marex@denx.de>