[U-Boot] "Writing to MMC(%d)... failed"

[Nathan]

I hope my last message didn't get lost during that outage last month.

In the mean time, I had to finagle the HardKernel code to work with
GCC 5.0 which ended up being only 1 line change which I may end up
encountering in mainline if I ever get far enough.
After transferring the "CONFIG_MMC_TRACE" to the HardKernel mmc.c, I
have a comparable output for the U2 with the "Samsung" mainline.

So the output comparison can be made more readable, I created a Google
Drive Sheet, lining up the output when there were repeats,
highlighting the differing output sections and changing the text color
for the different values:
https://docs.google.com/spreadsheets/d/1Gu10bG8wGJClorJjKoIMiAt4HR0nS22ugrL8-F5_Nbg/edit?usp=sharing