The "failed to set core voltage" error message should be harmless: I think either the device tree misses here the proper reference to the CPU current regulator and/or u-boot is compiled without the support for it.
As a result, u-boot is not able to change the voltage to the CPU and thus change its frequency from the default setting.
This is common when you use an image which gaana is compiled for a "close" device but not exactly the same.
A quick test you can do is to disable the UHS mode:
find in the source here device tree the strings starting with "sd-uhs-"
remove them.
Make a backup copy of the original DTB file and then convert back the DTS to DTB using dtc.
