^-- SC2153: Possible misspelling: BASELINE may not be assigned, but baseline is.

BASELINE is defined inside patches/config, but this confuses shellcheck.
According to https://github.com/koalaman/shellcheck/wiki/SC2153


the message doesn't appear for guarded references where if variable
is defined a default is used.

Maybe we should pick a better default like the git HEAD ?!

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Jani Nikula <jani.nikula@intel.com>