[coreboot] [patch] Fixed the LZMA compression flag in Kbuild

[Cristi Magherusan]

Please check the attached trivial patch.

It properly checks for the LZMA compression variable, and fixes a print
message for the VGA ROM that would print a useless NULL string.

Thanks,
Cristi

The patch is 
Signed-off by: Cristi Magherusan