SG: Change sg_set_page() to take length and offset argument

Most drivers need to set length and offset as well, so may as well fold
those three lines into one.

Add sg_assign_page() for those two locations that only needed to set
the page, where the offset/length is set outside of the function context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/drivers/block/cryptoloop.c b/drivers/block/cryptoloop.c
index 1b58b01..24116787 100644
--- a/drivers/block/cryptoloop.c
+++ b/drivers/block/cryptoloop.c
@@ -150,13 +150,8 @@
 		u32 iv[4] = { 0, };
 		iv[0] = cpu_to_le32(IV & 0xffffffff);
 
-		sg_set_page(&sg_in, in_page);
-		sg_in.offset = in_offs;
-		sg_in.length = sz;
-
-		sg_set_page(&sg_out, out_page);
-		sg_out.offset = out_offs;
-		sg_out.length = sz;
+		sg_set_page(&sg_in, in_page, sz, in_offs);
+		sg_set_page(&sg_out, out_page, sz, out_offs);
 
 		desc.info = iv;
 		err = encdecfunc(&desc, &sg_out, &sg_in, sz);