remove <linux/ata.h> include from <linux/hdreg.h>

All <linux/hdreg.h> users that need <linux/ata.h> have been fixed
to include it directly.

Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/hdreg.h

 #ifndef _LINUX_HDREG_H
 #define _LINUX_HDREG_H
 
-#ifdef __KERNEL__
-#include <linux/ata.h>
-#endif /* __KERNEL__ */
-
 #include <linux/types.h>
 
 /*