USB: cleanup for previous patches

This patch (as951) cleans up a few loose ends from earlier patches.
Redundant checks for non-NULL urb->dev are removed, as are checks of
urb->dev->bus (which can never be NULL).  Conversely, a check for
non-NULL urb->ep is added to the unlink paths.

A homegrown round-down-to-power-of-2 loop is simplified by using the
ilog2 routine.  The comparison in usb_urb_dir_in() is made more
transparent.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>