Fix type casts to meet libdevmapper.h declarations

--- lib/libdevmapper.c.orig	2007-12-22 13:28:36 +0300
+++ lib/libdevmapper.c	2007-12-22 13:29:11 +0300
@@ -42,7 +42,7 @@
 
 static int dm_init(void)
 {
-	dm_log_init(set_dm_error);
+	dm_log_init((dm_log_fn) set_dm_error);
 	if (!_dm_simple(DM_DEVICE_LIST_VERSIONS, "test")) {
 		set_error("Cannot communicate with device-mapper. Is the dm_mod module loaded?");
 		return -1;
@@ -470,7 +470,7 @@
 
 static const char *dm_get_dir(void)
 {
-	return dm_dir();
+	return (const char*) dm_dir();
 }
 
 struct setup_backend setup_libdevmapper_backend = {