SUNRPC: Remove redundant call to rpc_set_running() in __rpc_execute()

The RPC_TASK_RUNNING flag will always have been set in rpc_make_runnable()
once we get past the test for out_of_line_wait_on_bit() returning
ERESTARTSYS.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>