fastboot flash sparse image: buffer aligned

[qianfan]

Hi:

I'm testing 'fastboot flash' command with sparse images. Due to we write 
CHUNK_TYPE_RAW format data from unaligned buffer to mmc, the u-boot will 
report warinnig messages like this: "CACHE: Misaligned operation at 
range [84000028, 84001028]" if DCACHE is enabled. Is it a bug that we 
need fixed?

Thanks