Input: wacom - fix wacom_set_report retry logic

Logic sets a value and then reads it back to make sure it worked
and retries write on failures.  Since read and write share a buffer,
it needs to be set back up before writing though.

Issue is not seen a lot because 1) it doesn't need to retry for
a lot of tablets and 2) a lot of failures that need a retry are
from an -ETIMEDOUT and hopefully buffer is not touched in this case.

At least one user has shown logs with buffer being modified during
-ETIMEDOUT case with linux 3.7 kernel.

Signed-off-by: Chris Bagwell <chris@cnpbagwell.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>