Documentation/: it's -> its where appropriate

Fix obvious cases of "it's" being used when "its" was meant.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/Documentation/usb/WUSB-Design-overview.txt b/Documentation/usb/WUSB-Design-overview.txt
index c480e9c..4c5e379 100644
--- a/Documentation/usb/WUSB-Design-overview.txt
+++ b/Documentation/usb/WUSB-Design-overview.txt
@@ -381,7 +381,7 @@
 we issue another URB to read into the destination buffer the chunk of
 data coming out of the remote endpoint. Done, wait for the next guy. The
 callbacks for the URBs issued from here are the ones that will declare
-the xfer complete at some point and call it's callback.
+the xfer complete at some point and call its callback.
 
 Seems simple, but the implementation is not trivial.