USB: fix mos7840 problem with minor numbers

This patch fixes a problem with any mos7840 device where the use of the field "minor" before it is
initialised results in all the devices being overlaid in memory (minor = 0 for all instances)

Contributed by: Phillip Branch

Signed-off-by: Tony Cook <tony-cook@bigpond.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>