Since commit 7a049605 ("kbuild: fix DT binding schema rule to detect
command line changes"), this rule is every time re-run even if you change
nothing.

cmd_dtc takes one additional parameter to pass to the -O option of dtc.

We need to pass 'yaml' to if_changed_rule. Otherwise, cmd-check invoked
from if_changed_rule is false positive.

Fixes: 7a049605

 ("kbuild: fix DT binding schema rule to detect command line changes")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>