block: misc updates to blk_get_queue()

* blk_get_queue() is peculiar in that it returns 0 on success and 1 on
  failure instead of 0 / -errno or boolean.  Update it such that it
  returns %true on success and %false on failure.

* Make sure the caller checks for the return value.

* Separate out __blk_get_queue() which doesn't check whether @q is
  dead and put it in blk.h.  This will be used later.

This patch doesn't introduce any functional changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bsg.c

@@ -769,12 +769,10 @@ static struct bsg_device *bsg_add_device(struct inode *inode,
 					 struct file *file)
 {
 	struct bsg_device *bd;
-	int ret;
 #ifdef BSG_DEBUG
 	unsigned char buf[32];
 #endif
-	ret = blk_get_queue(rq);
-	if (ret)
+	if (!blk_get_queue(rq))
 		return ERR_PTR(-ENXIO);
 
 	bd = bsg_alloc_device();