USB: adutux: remove redundant variable minor

Variable minor is being assigned but never read, hence it is redundant
and can be removed. Cleans up clang warning:

drivers/usb/misc/adutux.c:770:2: warning: Value stored to 'minor' is
never read

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