platform/x86: dell_rbu: fix lock imbalance in img_update_realloc

We need to ensure rbu_data.lock is always held on return.

Fixes: 289790a3ea94 ("platform/x86: dell_rbu: stop abusing the DMA API")
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NStuart Hayes <stuart.w.hayes@gmail.com>
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NDarren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/dell_rbu.c

@@ -436,6 +436,7 @@ static int img_update_realloc(unsigned long size)
 	ordernum = get_order(size);
 	image_update_buffer =
 		(unsigned char *)__get_free_pages(GFP_DMA32, ordernum);
+	spin_lock(&rbu_data.lock);
 	if (!image_update_buffer) {
 		pr_debug("Not enough memory for image update:"
 			"size = %ld\n", size);
@@ -446,7 +447,6 @@ static int img_update_realloc(unsigned long size)
 	if (WARN_ON_ONCE(img_buf_phys_addr > BIOS_SCAN_LIMIT))
 		return -EINVAL; /* can't happen per definition */
 
-	spin_lock(&rbu_data.lock);
 	rbu_data.image_update_buffer = image_update_buffer;
 	rbu_data.image_update_buffer_size = size;
 	rbu_data.bios_image_size = rbu_data.image_update_buffer_size;