usb: Correct CLEAR_FEATURE code in ehci-hcd

This commit broke USB2 on link (Chromebook Pixel):

  020bbcb7 usb: hub: Power-cycle on root-hub ports

However the root cause seems to be a missing mask and missing 'break'
in ehci-hcd.c. This patch fixes both.

On link, 'usb start' with a USB keyboard and memory stick inserted now
finds both. The keyboard works as expected. Also ext2ls shows a directory
listing from the memory stick.

Signed-off-by: Simon Glass <sjg@chromium.org>