usb: host: fix incorrect updating of offset

The variable temp is incorrectly being updated, instead it should
be offset otherwise the loop just reads the same capability value
and loops forever.  Thanks to Alan Stern for pointing out the
correct fix to my original fix.  Fix also cleans up clang warning:

drivers/usb/host/ehci-dbg.c:840:4: warning: Value stored to 'temp'
is never read

Fixes: d49d4317 ("USB: misc ehci updates")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>