Makefile: Correctly propagate failure when removing target

On more places is used pattern 'command > $@ || rm -f $@'. But it does not
propagate failure from 'command' as 'rm -f' returns success.

Fix it by calling 'false' to correctly propagate failure after 'rm -f'.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>