doc: spelling error changes

Fixed multiple spelling errors.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Carlos E. Garcia <carlos@cgarcia.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/input/input.txt b/Documentation/input/input.txt
index 666c06c..0acfddb 100644
--- a/Documentation/input/input.txt
+++ b/Documentation/input/input.txt
@@ -226,7 +226,7 @@
 ~~~~~~~~~~~
   evdev is the generic input event interface. It passes the events
 generated in the kernel straight to the program, with timestamps. The
-API is still evolving, but should be useable now. It's described in
+API is still evolving, but should be usable now. It's described in
 section 5. 
 
   This should be the way for GPM and X to get keyboard and mouse