[Yaffs] YAFFS1 return zero for success in commit_write

Some callers to block-layer commit_write function treat non-zero
return as error, notably the loopback mount driver sometimes used in
conjunction with YAFFS on NAND flash for bad block avoidance, etc.
Return zero for success as do various other commit_write functions.

Signed-off-by: Todd Poynor <tpoynor@mvista.com>

Index: yaffs_fs.c
===================================================================
RCS file: /home/aleph1/cvs/yaffs/yaffs_fs.c,v
retrieving revision 1.41
diff -u -r1.41 yaffs_fs.c
--- yaffs_fs.c    11 Oct 2005 23:43:27 -0000    1.41
+++ yaffs_fs.c    19 Oct 2005 03:04:34 -0000
@@ -596,9 +596,9 @@
         SetPageUptodate(pg);
     }

-    T(YAFFS_TRACE_OS,("yaffs_commit_write returning %d\n",nWritten));
-    
-    return nWritten;
+    T(YAFFS_TRACE_OS,("yaffs_commit_write returning %d\n",nWritten == nBytes ? 0 : -1));
+
+    return nWritten == nBytes ? 0 : -1;

}