doc: Fix typo in doucmentations

Correct typo (double words) in documentations.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/virtual/kvm/api.txt

@@ -53,7 +53,7 @@ incompatible change are allowed.  However, there is an extension
 facility that allows backward-compatible extensions to the API to be
 queried and used.
 
-The extension mechanism is not based on on the Linux version number.
+The extension mechanism is not based on the Linux version number.
 Instead, kvm defines extension identifiers and a facility to query
 whether a particular extension identifier is available.  If it is, a
 set of ioctls is available for application use.