buildroot

support/tests: fix ext4 runtime test

The current test fails because of a legacy option, renamed during the
recent ext overhaul.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Cc: Samuel Martin <s.martin49@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>