drm: Fix missing unlock and free on error in drm_legacy_addbufs_pci()

Add the missing unlock and free before return from function
drm_legacy_addbufs_pci() in the error handling case.

Fixes: 70556e24 ("drm: remove usage of drm_pci_alloc/free")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1621341302-112089-1-git-send-email-zou_wei@huawei.com

drivers/gpu/drm/drm_bufs.c

@@ -984,8 +984,16 @@ int drm_legacy_addbufs_pci(struct drm_device *dev,
 
 	while (entry->buf_count < count) {
 		dmah = kmalloc(sizeof(drm_dma_handle_t), GFP_KERNEL);
-		if (!dmah)
+		if (!dmah) {
+			/* Set count correctly so we free the proper amount. */
+			entry->buf_count = count;
+			entry->seg_count = count;
+			drm_cleanup_buf_error(dev, entry);
+			kfree(temp_pagelist);
+			mutex_unlock(&dev->struct_mutex);
+			atomic_dec(&dev->buf_alloc);
 			return -ENOMEM;
+		}
 
 		dmah->size = total;
 		dmah->vaddr = dma_alloc_coherent(dev->dev,