Fix a filename logging in nfs4_op_open

Signed-off-by: Malahal Naineni <malahal@us.ibm.com>
Acked-by: Frank S. Filz <ffilzlnx@mindspring.com>
Reviewed-by: Venkateswararao Jujjuri (JV) <jvrao@linux.vnet.ibm.com>