crypto: ccp - Fix sparse, use plain integer as NULL pointer

Fix sparse warning: Using plain integer as NULL pointer. Replaces
assignment of 0 to pointer with NULL assignment.

Fixes: 200664d5237f (Add Secure Encrypted Virtualization ...)
Cc: Borislav Petkov <bp@suse.de>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Gary Hook <gary.hook@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/ccp/psp-dev.c

@@ -211,7 +211,7 @@ static int __sev_platform_shutdown_locked(int *error)
 {
 	int ret;
 
-	ret = __sev_do_cmd_locked(SEV_CMD_SHUTDOWN, 0, error);
+	ret = __sev_do_cmd_locked(SEV_CMD_SHUTDOWN, NULL, error);
 	if (ret)
 		return ret;
 
@@ -271,7 +271,7 @@ static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
 			return rc;
 	}
 
-	return __sev_do_cmd_locked(SEV_CMD_FACTORY_RESET, 0, &argp->error);
+	return __sev_do_cmd_locked(SEV_CMD_FACTORY_RESET, NULL, &argp->error);
 }
 
 static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
@@ -299,7 +299,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
 			return rc;
 	}
 
-	return __sev_do_cmd_locked(cmd, 0, &argp->error);
+	return __sev_do_cmd_locked(cmd, NULL, &argp->error);
 }
 
 static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
@@ -624,7 +624,7 @@ EXPORT_SYMBOL_GPL(sev_guest_decommission);
 
 int sev_guest_df_flush(int *error)
 {
-	return sev_do_cmd(SEV_CMD_DF_FLUSH, 0, error);
+	return sev_do_cmd(SEV_CMD_DF_FLUSH, NULL, error);
 }
 EXPORT_SYMBOL_GPL(sev_guest_df_flush);