Recently tried the latest standard release of u-boot from ftp://ftp.denx.de/pub/u-boot/ , and it now works OK with the SDCard in the Odroid U3.    You still have to incorporate the ‘special’ secure-boot binaries and shell script from the hardkernel version ( in directory sd_fuse) from https://github.com/hardkernel/u-boot/tree/odroid-v2010.12 and change the reference to u-boot.bin to u-boot-dtb.bin in sd_fusing.sh.

U-Boot 2015.10-rc3 (Sep 22 2015 - 15:33:07 -0700)

CPU: Exynos4412 @ 1 GHz
Model: Odroid based on Exynos4412
Board: Odroid based on Exynos4412
Model: u3
DRAM: 2 GiB
LDO20@VDDQ_EMMC_1.8V: set 1800000 uV; enabling
LDO22@VDDQ_EMMC_2.8V: set 2800000 uV; enabling
LDO21@TFLASH_2.8V: set 2800000 uV; enabling
MMC: SAMSUNG SDHCI: 0, EXYNOS DWMMC: 1
Net: No ethernet found.
Hit any key to stop autoboot: 0

Then the kernel boots OK..

Fedora 23 (Twenty Three)
Kernel 4.3.0-rc2 on an armv7l (ttySAC1)
.................
]# uname -a
Linux rgodroid 4.3.0-rc2 #1 SMP Mon Sep 21 13:38:23 PDT 2015 armv7l armv7l armv7l GNU/Linux

Robert Gadsdon.   September 25, 2015