superiotool: Don't compile with -Werror

superiotool: Don't compile with -Werror

Older libpci version have headers using 'long long' which isn't allowed
in ANSI C. Since we cannot control the libpci version installed in the
system nor in generall have complete control over system headers, simply
skip using -Werror in our makefile.

Change-Id: Ibc1e57bef033bf4971f4108d078222dcf168d5e3
Signed-off-by: Mathias Krause <mathias.krause@secunet.com>
Reviewed-on: http://review.coreboot.org/210
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>