block: Really silence spurious compiler warnings

The uninitialized_var() macro appears to not work on structs...
Get rid of it, and manually initialize instead.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-merge.c

@@ -86,11 +86,9 @@ EXPORT_SYMBOL(blk_recount_segments);
 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
 				   struct bio *nxt)
 {
-	struct bio_vec end_bv, nxt_bv;
+	struct bio_vec end_bv = { NULL }, nxt_bv;
 	struct bvec_iter iter;
 
-	uninitialized_var(end_bv);
-
 	if (!blk_queue_cluster(q))
 		return 0;
 
@@ -170,13 +168,11 @@ __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
 		  struct scatterlist *sglist)
 {
-	struct bio_vec bvec, bvprv;
+	struct bio_vec bvec, bvprv = { NULL };
 	struct req_iterator iter;
 	struct scatterlist *sg;
 	int nsegs, cluster;
 
-	uninitialized_var(bvprv);
-
 	nsegs = 0;
 	cluster = blk_queue_cluster(q);
 
@@ -234,13 +230,11 @@ EXPORT_SYMBOL(blk_rq_map_sg);
 int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
 		   struct scatterlist *sglist)
 {
-	struct bio_vec bvec, bvprv;
+	struct bio_vec bvec, bvprv = { NULL };
 	struct scatterlist *sg;
 	int nsegs, cluster;
 	struct bvec_iter iter;
 
-	uninitialized_var(bvprv);
-
 	nsegs = 0;
 	cluster = blk_queue_cluster(q);