Rationalize fasync return values

Most fasync implementations do something like:

     return fasync_helper(...);

But fasync_helper() will return a positive value at times - a feature used
in at least one place.  Thus, a number of other drivers do:

     err = fasync_helper(...);
     if (err < 0)
             return err;
     return 0;

In the interests of consistency and more concise code, it makes sense to
map positive return values onto zero where ->fasync() is called.

Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 516925d..b4ef2f8 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1154,7 +1154,6 @@
 static int
 sg_fasync(int fd, struct file *filp, int mode)
 {
-	int retval;
 	Sg_device *sdp;
 	Sg_fd *sfp;
 
@@ -1163,8 +1162,7 @@
 	SCSI_LOG_TIMEOUT(3, printk("sg_fasync: %s, mode=%d\n",
 				   sdp->disk->disk_name, mode));
 
-	retval = fasync_helper(fd, filp, mode, &sfp->async_qp);
-	return (retval < 0) ? retval : 0;
+	return fasync_helper(fd, filp, mode, &sfp->async_qp);
 }
 
 static int