9p: Kill set but unused variable in 9p_client_{read,write}() and p9_client_readdir()

Fixes the following warnings:

net/9p/client.c:1305:18: warning: variable ‘total’ set but not used [-Wunused-but-set-variable]
net/9p/client.c:1370:18: warning: variable ‘total’ set but not used [-Wunused-but-set-variable]
net/9p/client.c:1769:18: warning: variable ‘total’ set but not used [-Wunused-but-set-variable]

Signed-off-by: David S. Miller <davem@davemloft.net>