net/9p: correct the variable name in v9fs_get_trans_by_name() comment

The v9fs_get_trans_by_name(char *s) variable name is not "name" but "s".

Signed-off-by: Sun Lianwen <sunlw.fnst@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>