doc: kbuild: fix default in `imply` table

`BAZ` takes `FOO`'s value as default (as far as `BAR` allows it).

Signed-off-by: Miguel Ojeda <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

Documentation/kbuild/kconfig-language.rst

···
 	y		y		y		Y/m/n
 	n		m		n		N/m
 	m		m		m		M/n
-	y		m		n		M/n
+	y		m		m		M/n
 	y		n		*		N
 	===		===		=============	==============