nfs/blocklayout: Use the passed in gfp flags

This allocation should use the passed in GFP_ flags instead of
GFP_KERNEL.  One places where this matters is in filelayout_pg_init_write()
which uses GFP_NOFS as the allocation flags.

Fixes: 5c83746a ("pnfs/blocklayout: in-kernel GETDEVICEINFO XDR parsing")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>