crypto: ccp - Get a free page to use while fetching initial nonce

dbc_dev_init() gets a free page from `GFP_KERNEL`, but if that page has
any data in it the first nonce request will fail.
This prevents dynamic boost control from probing. To fix this, explicitly
request a zeroed page with `__GFP_ZERO` to ensure first nonce fetch works.

Fixes: c04cf9e1 ("crypto: ccp - Add support for fetching a nonce for dynamic boost control")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/ccp/dbc.c

@@ -205,7 +205,7 @@ int dbc_dev_init(struct psp_device *psp)
 		return -ENOMEM;
 
 	BUILD_BUG_ON(sizeof(union dbc_buffer) > PAGE_SIZE);
-	dbc_dev->mbox = (void *)devm_get_free_pages(dev, GFP_KERNEL, 0);
+	dbc_dev->mbox = (void *)devm_get_free_pages(dev, GFP_KERNEL | __GFP_ZERO, 0);
 	if (!dbc_dev->mbox) {
 		ret = -ENOMEM;
 		goto cleanup_dev;