socrates_cyclone5_defconfig: U-Boot needs DTC

Probably not noticed before because dtc was already built or it was
installed on the host.

Fixes: https://gitlab.com/arnout/buildroot/-/jobs/28979369

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Michał Łyszczek <michal.lyszczek@bofc.pl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

configs/socrates_cyclone5_defconfig

@@ -21,6 +21,7 @@ BR2_TARGET_UBOOT_CUSTOM_GIT=y
 BR2_TARGET_UBOOT_CUSTOM_REPO_URL="https://github.com/altera-opensource/u-boot-socfpga.git"
 BR2_TARGET_UBOOT_CUSTOM_REPO_VERSION="v2017.07"
 BR2_TARGET_UBOOT_BOARD_DEFCONFIG="socfpga_socrates"
+BR2_TARGET_UBOOT_NEEDS_DTC=y
 BR2_TARGET_UBOOT_FORMAT_IMG=y
 BR2_TARGET_UBOOT_SPL=y
 BR2_TARGET_UBOOT_ALTERA_SOCFPGA_IMAGE_CRC=y