mremap: Do nothing when no size change and !MREMAP_FIXED

Behave in the same way as Linux which returns old_address when
old_size == new_size && !MREMAP_FIXED.

Refs: #1112
Change-Id: Ice1421a8a77f962d087de8475aa2cd40c59be5f7

kernel/syscall.c

@@ -7736,6 +7736,14 @@ SYSCALL_DECLARE(mremap)
 		goto out;
 	}
 
+	/* check necessity of remap */
+	if (!(flags & MREMAP_FIXED) && oldsize == newsize) {
+		/* Nothing to do */
+		error = 0;
+		newstart = oldaddr;
+		goto out;
+	}
+
 	if (oldend < oldstart) {
 		error = -EINVAL;
 		ekprintf("sys_mremap(%#lx,%#lx,%#lx,%#x,%#lx):"