Fix some typos in Documentation/: 'A'

This patch fixes typos in various Documentation txts.
This patch addresses some words starting with the letter 'A'.

Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
diff --git a/Documentation/md.txt b/Documentation/md.txt
index 9ae9e40..13aa401a 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -175,7 +175,7 @@
      raid levels that involve striping (1,4,5,6,10). The address space
      of the array is conceptually divided into chunks and consecutive
      chunks are striped onto neighbouring devices.
-     The size should be atleast PAGE_SIZE (4k) and should be a power
+     The size should be at least PAGE_SIZE (4k) and should be a power
      of 2.  This can only be set while assembling an array
 
   component_size