Silence newer gcc warnings.

Newer versions of gcc generate "might not be initialized" warnings for
several variables in nfsrpc_doiods(). I have checked and all of these
variables are assigned values before they are used.
In the one case of "tdrpc", it could have passed garbage as an argument
to nfscl_dofflayoutio() when mirrorcnt is one. However nfscl_dofflayoutio() only
uses the argument when mirrorcnt > 1, so it wasn't actually broken.
This patch initializes "tdrpc" to avoid confusion and initializes the rest
to make the compiler happy.

Requested by: mmacy