nfs41: .init_read and .init_write can be called with valid pg_lseg
nfs41: .init_read and .init_write can be called with valid pg_lseg

With pgio refactoring in v3.15, .init_read and .init_write can be
called with valid pgio->pg_lseg. file layout was fixed at that time
by commit c6194271f (pnfs: filelayout: support non page aligned
layouts). But the generic helper still needs to be fixed.

Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org # 3.15+
Signed-off-by: Peng Tao <4fb2b5cc20694ed9d470f738b651303a1e636b2d@primarydata.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs