configs/sipeed_maix*sdcard: add missing quotes around string option
The build of those 4 defconfigs was failing in Gitlab CI as the
defconfig check doesn't pass, due to the BR2_TARGET_ROOTFS_EXT2_SIZE
string option value missing double quotes:
WARN: defconfig ./configs/sipeed_maixduino_sdcard_defconfig can't be used:
Missing: BR2_TARGET_ROOTFS_EXT2_SIZE=64M
Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/2812054080 (sipeed_maixduino_sdcard_defconfig)
https://gitlab.com/buildroot.org/buildroot/-/jobs/2812054070 (sipeed_maix_go_sdcard_defconfig)
https://gitlab.com/buildroot.org/buildroot/-/jobs/2812054049 (sipeed_maix_dock_sdcard_defconfig)
https://gitlab.com/buildroot.org/buildroot/-/jobs/2812054037 (sipeed_maix_bit_sdcard_defconfig)
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>