kbuild: add hint about __refdata to modpost

As requested by Guennadi Liakhovetski

Cc: Guennadi Liakhovetski <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>

scripts/mod/modpost.c

···
 		"The variable %s references\n"
 		"the %s %s%s%s\n"
 		"If the reference is valid then annotate the\n"
-		"variable with __init* (see linux/init.h) "
+		"variable with __init* or __refdata (see linux/init.h) "
 		"or name the variable:\n",
 		fromsym, to, sec2annotation(tosec), tosym, to_p);
 		while (*s)