Fix warnings (see also https://trac.osgeo.org/grass/changeset/67518)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@67559 15284696-431f-4ddb-bdfa-cd5b030d7da7

include/defs/sqlp.h

@@ -2,7 +2,7 @@
 #define GRASS_SQLPDEFS_H
 
 int my_yyinput(char *buf, int max_size);
-void yyerror(char *s);
+void yyerror(const char *s);
 int yyparse();
 int yywrap();
 

lib/db/sqlp/sqlp.l

@@ -256,7 +256,7 @@ int my_yyinput(char *buf, int max_size)
  * message and deposits it in a usefull place.
  *
  **********************************************************************/
-void yyerror( char *s )
+void yyerror( const char *s )
 {
 	snprintf( sqlpStmt->errmsg, 500, "%s processing '%s'", s, yytext );