staging/winbond: use err and remove nr

err can be used get return status of the  usb_control_msg, rather using
nr and assigning it to err when the function returns error.

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>