Compilation of mtd_test.ko should be added only for kernel 6.6 or above.
Fixes 26df88a ("kernel: Add kmod-mfd-test")
Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Link: https://github.com/openwrt/openwrt/pull/16085
Signed-off-by: Robert Marko <robimarko@gmail.com>