USB: whci-hcd: make endpoint_reset method async

usb_hcd_endpoint_reset() may be called in atomic context and must not
sleep.  So make whci-hcd's endpoint_reset() asynchronous.  URBs
submitted while the reset is in progress will be queued (on the std
list) and transfers will resume once the reset is complete.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>