bitmap API (include/linux/bitmap.h) has 'bitmap' prefix for its methods.

On the other hand MD bitmap API is special case.
Adding 'md' prefix to it to avoid name space collision.

No functional changes intended.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: NShaohua Li <shli@kernel.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>