Fix compiler warning in setup_translation().

Assign 'desc' just to silence compiler warning.
diff --git a/src/block.c b/src/block.c
index 0a65ae6..d36ad36 100644
--- a/src/block.c
+++ b/src/block.c
@@ -86,7 +86,7 @@
     u16 cylinders = GET_GLOBAL(drive_g->pchs.cylinders);
     u16 spt = GET_GLOBAL(drive_g->pchs.spt);
     u64 sectors = GET_GLOBAL(drive_g->sectors);
-    const char *desc;
+    const char *desc = NULL;
 
     switch (translation) {
     default: