drivers: usb_dc_kinetis: fix out-of-bounds write/read

Fix out-of-bounds write/read.

fixes: #7714
fixes: #7715
fixes: #7719
fixes: #7721
fixes: #7723
fixes: #7725
fixes: #7727
fixes: #7734
fixes: #7738

Coverity-ID: 186032
Coverity-ID: 186036
Coverity-ID: 186044
Coverity-ID: 186046
Coverity-ID: 186048
Coverity-ID: 186051
Coverity-ID: 186055
Coverity-ID: 186059
Coverity-ID: 186061

Signed-off-by: Johann Fischer <j.fischer@phytec.de>