USB: ene_usb6250: fix SCSI residue overwriting

In the ene_usb6250 sub-driver for usb-storage, the SCSI residue is not
reported correctly.  The residue is initialized to 0, but this value
is overwritten whenever the driver sends firmware to the card reader
before performing the current command.  As a result, a valid READ or
WRITE operation appears to have failed, causing the SCSI core to retry
the command multiple times and eventually fail.

This patch fixes the problem by resetting the SCSI residue to 0 after
sending firmware to the device.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: Andreas Hartmann <andihartmann@01019freenet.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>