[BLOCK] Fix failing compile with BLK_DEV_IO_TRACE=n

I get a compilation error in sglist-arch branch
with BLK_DEV_IO_TRACE=n:

  CC      block/compat_ioctl.o
/usr0/export/dev/bharrosh/git/pub/linux-2.6-block/block/compat_ioctl.c: In
function ?compat_blk_trace_setup?:
/usr0/export/dev/bharrosh/git/pub/linux-2.6-block/block/compat_ioctl.c:568:
error: expected expression before ?do?
make[2]: *** [block/compat_ioctl.o] Error 1

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/linux/blktrace_api.h

@@ -290,7 +290,12 @@ static inline void blk_add_trace_remap(struct request_queue *q, struct bio *bio,
 #define blk_add_trace_generic(q, rq, rw, what)	do { } while (0)
 #define blk_add_trace_pdu_int(q, what, bio, pdu)	do { } while (0)
 #define blk_add_trace_remap(q, bio, dev, f, t)	do {} while (0)
-#define do_blk_trace_setup(q, bdev, buts)	do {} while (0)
+static inline int do_blk_trace_setup(struct request_queue *q,
+				     struct block_device *bdev,
+				     struct blk_user_trace_setup *buts)
+{
+	return 0;
+}
 #endif /* CONFIG_BLK_DEV_IO_TRACE */
 #endif /* __KERNEL__ */
 #endif