init/do_mounts.c: print error code on mount failure

Printing the error code makes it easier to debug the cause of a mount
failure.  For example I had the problem that the root file system could
not be mounted read-writeable because my SD card was write-protected.
Without an error code it looks like the SD card was not detected at all.

Signed-off-by: Bernhard Walle <bernhard@bwalle.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/do_mounts.c

@@ -373,8 +373,8 @@ retry:
 #ifdef CONFIG_BLOCK
 		__bdevname(ROOT_DEV, b);
 #endif
-		printk("VFS: Cannot open root device \"%s\" or %s\n",
-				root_device_name, b);
+		printk("VFS: Cannot open root device \"%s\" or %s: error %d\n",
+				root_device_name, b, err);
 		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
 
 		printk_all_partitions();