NFS: Create a common pgio_error function

At this point, the read and write versions of this function look
identical so both should use the same function.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --cc fs/nfs/internal.h
Simple merge

diff --cc fs/nfs/pagelist.c
Simple merge

diff --cc fs/nfs/read.c
Simple merge

diff --cc fs/nfs/write.c
Simple merge