USB: fix warning caused by autosuspend counter going negative

This patch (as937) fixes a minor bug in the autosuspend usage-counting
code.  Each hub's usage counter keeps track of the number of
unsuspended children.  However the current driver increments the
counter after registering a new child, by which time the child may
already have been suspended and caused the counter to go negative.
The obvious solution is to increment the counter before registering
the child.

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