trival: md_k.h should be md.h in the beginning comment of file md.h

Signed-off-by: NWang Sheng-Hui <shhuiw@gmail.com>
Signed-off-by: NNeilBrown <neilb@suse.de>

drivers/md/md.h

 /*
-   md_k.h : kernel internal structure of the Linux MD driver
+   md.h : kernel internal structure of the Linux MD driver
           Copyright (C) 1996-98 Ingo Molnar, Gadi Oxman
 	  
    This program is free software; you can redistribute it and/or modify