USB: isight: fix kernel bug when loading firmware

We were sending data on the stack when uploading firmware, which causes
some machines fits, and is not allowed.  Fix this by using the buffer we
already had around for this very purpose.

Reported-by: Wouter M. Koolen <wmkoolen@cwi.nl>
Tested-by: Wouter M. Koolen <wmkoolen@cwi.nl>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>