NFS: Fix initialisation of I/O result struct in nfs_pgio_rpcsetup

[ Upstream commit 17d8c5d145000070c581f2a8aa01edc7998582ab ]

Initialise the result count to 0 rather than initialising it to the
argument count. The reason is that we want to ensure we record the
I/O stats correctly in the case where an error is returned (for
instance in the layoutstats).

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>