staging: nvec: Do not print free message for tx_scratch

The scratch area is not part of the pool and thus gets
no allocation message. Printing a free message would
be confusing, and the pointer subtraction would be
undefined behavior.

Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>