term/ieee1275/serial: Fix memory leak

The grub_zalloc() allocates memory for port. If the allocation for
port->name fails the function returns NULL without freeing the
previously allocated port memory. This results in a memory leak.
To avoid this we must free port before return.

Signed-off-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/term/ieee1275/serial.c

@@ -236,7 +236,11 @@ add_port (struct ofserial_hash_ent *ent)
 			    + grub_strlen (ent->shortest));
   port->elem = ent;
   if (!port->name)
-    return NULL;
+    {
+      grub_free (port);
+      return NULL;
+    }
+
   ptr = grub_stpcpy (port->name, "ieee1275/");
   grub_strcpy (ptr, ent->shortest);