USB: check serial-number string after device reset

This patch (as1048) extends the descriptor checking after a device is
reset.  Now the SerialNumber string descriptor is compared to its old
value, in addition to the device and configuration descriptors.

As a consequence, the kmalloc() call in usb_string() is now on the
error-handling pathway for usb-storage.  Hence its allocation type is
changed to GFO_NOIO.

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