rkcommon.c: Drop pointless assignment

Assigning a variable to itself is not necessary. Drop this and also add a
check for malloc() failure.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Coverity (CID: 161418)
Fixes: 111bcc4f (rockchip: mkimage: pad the header to 8-bytes (using a 'nop') for RK3399)

tools/rkcommon.c

@@ -380,8 +380,9 @@ int rkcommon_vrec_header(struct image_tool_params *params,
 
 	/* Allocate, clear and install the header */
 	tparams->hdr = malloc(tparams->header_size);
+	if (!tparams->hdr)
+		return -ENOMEM;
 	memset(tparams->hdr, 0, tparams->header_size);
-	tparams->header_size = tparams->header_size;
 
 	/*
 	 * If someone passed in 0 for the alignment, we'd better handle