Documentation: Fix typo in power-management.txt

Correct spelling "diconnect()" to "disconnect()" in
Documentation/usb/power-management.txt

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/usb/power-management.txt

@@ -345,7 +345,7 @@ autosuspend the device.
 Drivers need not be concerned about balancing changes to the usage
 counter; the USB core will undo any remaining "get"s when a driver
 is unbound from its interface.  As a corollary, drivers must not call
-any of the usb_autopm_* functions after their diconnect() routine has
+any of the usb_autopm_* functions after their disconnect() routine has
 returned.
 
 Drivers using the async routines are responsible for their own