amd/cimx/rd890/amd.h: Eliminate redefinition of NULL

This change replaces a redefinition of NULL with the standard
definition from <stddef.h> to eliminate a compiler redefinition
warning.

Change-Id: I441fa569f545c0efb00284b5ee58aa27cb6617ba
Signed-off-by: Bruce Griffith <Bruce.Griffith@se-eng.com>
Reviewed-on: http://review.coreboot.org/3540
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed