[coreboot] PATCH: fix for flashrom makefile when CFLAGS are specified on command line.

[Clark Rawlins]

With this small change it is possible to build flashrom again when
specifying custom CFLAGS from the make command line like:

make CFLAGS="..."

I need to do this when building flashrom in a cross compiler environment
like buildroot for a foreign target.

Signed-of-by: Clark Rawlins

Please guide me if I have not completed all the required steps or if my
patch isn't quite ready.

Clark