modpost: constify *modname function argument where possible

Neither find_module() nor read_symbols() does change *modname.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 9e70a6a..1663fb1 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -121,7 +121,7 @@
 /* A list of all modules we processed */
 static struct module *modules;
 
-static struct module *find_module(char *modname)
+static struct module *find_module(const char *modname)
 {
 	struct module *mod;
 
@@ -1929,7 +1929,7 @@
 	return s;
 }
 
-static void read_symbols(char *modname)
+static void read_symbols(const char *modname)
 {
 	const char *symname;
 	char *version;