USB: isight: fix kernel bug when loading firmware

commit 59bf5cf9 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>