Fix fallout after generated defconfig support

Fix improper use of qstrip; use correct variables.

Fixes #8546.

Reported-by:  <craigswank@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>