md: fix typos for stipe

Signed-off-by: NGuoqing Jiang <gqjiang@suse.com>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/bitmap.h

@@ -49,8 +49,8 @@
  * When we set a bit, or in the counter (to start a write), if the fields is
  * 0, we first set the disk bit and set the counter to 1.
  *
- * If the counter is 0, the on-disk bit is clear and the stipe is clean
- * Anything that dirties the stipe pushes the counter to 2 (at least)
+ * If the counter is 0, the on-disk bit is clear and the stripe is clean
+ * Anything that dirties the stripe pushes the counter to 2 (at least)
  * and sets the on-disk bit (lazily).
  * If a periodic sweep find the counter at 2, it is decremented to 1.
  * If the sweep find the counter at 1, the on-disk bit is cleared and the