nommu: fix an incorrect comment in the do_mmap_shared_file()

Fix an incorrect comment in the do_mmap_shared_file().  If a mapping is
requested MAP_SHARED, then a private copy cannot be made and still provide
correct semantics.
Signed-off-by: David Howells <dhowells@redhat.com>
Reported-by: Dave Hudson <uclinux@blueteddy.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/nommu.c

@@ -1040,10 +1040,9 @@ static int do_mmap_shared_file(struct vm_area_struct *vma)
 	if (ret != -ENOSYS)
 		return ret;
 
-	/* getting an ENOSYS error indicates that direct mmap isn't
-	 * possible (as opposed to tried but failed) so we'll fall
-	 * through to making a private copy of the data and mapping
-	 * that if we can */
+	/* getting -ENOSYS indicates that direct mmap isn't possible (as
+	 * opposed to tried but failed) so we can only give a suitable error as
+	 * it's not possible to make a private copy if MAP_SHARED was given */
 	return -ENODEV;
 }