am335x: Unable to boot u-boot image from mmc1

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Hi all,

I try to build u-boot by config of am335x_evm_test_defconfig on branch
master and burn to sd card on beaglebone black.

When I boot the device, the print the string "Trying to boot from MMC1".

But I build u-boot by config of am335x_evm_test_defconfig on branch
v2019.04 and boot normally.

Thanks. Regards.