block: fix segment split

Inside blk_bio_segment_split(), previous bvec pointer(bvprvp)
always points to the iterator local variable, which is obviously
wrong, so fix it by pointing to the local variable of 'bvprv'.

Fixes: 5014c31(block: fix bogus compiler warnings in blk-merge.c)
Cc: [email protected] #4.3
Reported-by: Michael Ellerman <[email protected]>
Reported-by: Mark Salter <[email protected]>
Tested-by: Laurent Dufour <[email protected]>
Tested-by: Mark Salter <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: Ming Lei

block/blk-merge.c

@@ -98,7 +98,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 
 			seg_size += bv.bv_len;
 			bvprv = bv;
-			bvprvp = &bv;
+			bvprvp = &bvprv;
 			sectors += bv.bv_len >> 9;
 			continue;
 		}
@@ -108,7 +108,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 
 		nsegs++;
 		bvprv = bv;
-		bvprvp = &bv;
+		bvprvp = &bvprv;
 		seg_size = bv.bv_len;
 		sectors += bv.bv_len >> 9;
 	}