Constify command options

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1694)
diff --git a/apps/dsa.c b/apps/dsa.c
index 6aef502..f608d7d 100644
--- a/apps/dsa.c
+++ b/apps/dsa.c
@@ -34,7 +34,7 @@
     OPT_PUBOUT, OPT_CIPHER, OPT_PASSIN, OPT_PASSOUT
 } OPTION_CHOICE;
 
-OPTIONS dsa_options[] = {
+const OPTIONS dsa_options[] = {
     {"help", OPT_HELP, '-', "Display this summary"},
     {"inform", OPT_INFORM, 'f', "Input format, DER PEM PVK"},
     {"outform", OPT_OUTFORM, 'F', "Output format, DER PEM PVK"},