Makefiles.rules: Silence cmp
Makefiles.rules: Silence cmp

When building with stdout redirected to /dev/null:
make buildall -j >/dev/null

One would still see "error" message like:
cmp: build/hammer/ec_version.h: No such file or directory

BRANCH=none
BUG=none
TEST=make buildall -j > /dev/null is quiet again.

Change-Id: I3ee9d090d3d46a70a096db0bebbfecaf293dca6d
Signed-off-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1141448
Commit-Ready: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Tested-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>
Reviewed-by: Patrick Georgi <bc411205f21846a74924ee7b489c75617ec76078@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec