usb: misc: adutux: remove redundant error check on copy_to_user return code

The 2nd check for a non-zero return from copy_to_user is redundant as
it is has already been made a few lines earlier.  This check was made
redundant because of previous fix to the copy_to_user error return
check.

Detected by CoverityScan, CID#114347 ("Logically Dead Code")

Fixes: 1865a9c3 ("USB: adutux: fix misuse of return value of copy_to_user()")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>