NET: ROSE: Don't use static buffer.

The use of a static buffer in rose2asc() to return its result is not
threadproof and can result in corruption if multiple threads are trying
to use one of the procfs files based on rose2asc().

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>