USB: FHCI: Fix build after kfifo rework

After kfifo rework FHCI fails to build:

  CC      drivers/usb/host/fhci-tds.o
drivers/usb/host/fhci-tds.c: In function 'fhci_ep0_free':
drivers/usb/host/fhci-tds.c:108: error: used struct type value where scalar is required
drivers/usb/host/fhci-tds.c:118: error: used struct type value where scalar is required
drivers/usb/host/fhci-tds.c:128: error: used struct type value where scalar is required

This is because kfifos are no longer pointers in the ep struct.
So, instead of checking the pointers, we should now check if kfifo
is initialized.

Reported-by: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>