USB: CP210X Use official request code definitions

The CP210X driver was developed without official device specifications.
This has lead to an incorrect assumption that all GET request codes are
equal to the corresponding SET request code +1.
This patch removes this incorrect assumption, and uses request code
definitions based on the updated GPL driver from SiLabs.
This modification is needed before extended functionality such as GPIO
on CP2103 can be supported.

Signed-off-by: Craig Shelley <craig@microtron.org.uk>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>