USB: fix typo in documentation

A typo sneaked in the latest change on the USB documentation. Fixing it
and also a trailing whitespace since it is also in the "USB Host-Side API
Model" chapter.
Signed-off-by: NLuis de Bethencourt <luisbg@osg.samsung.com>

Documentation/DocBook/usb.tmpl

@@ -168,7 +168,7 @@
     Device driver authors should make a point of doing disconnect
     testing (while the device is active) with each different host
     controller driver, to make sure drivers don't have bugs of
-    thei1r own as well as to make sure they aren't relying on some
+    their own as well as to make sure they aren't relying on some
     HCD-specific behavior.
     </para>