efi_loader: efi_variable_parse_signature() returns NULL on error

[Patrick Wildt]

efi_variable_parse_signature() returns NULL on error, so IS_NULL()
is an incorrect check.  The goto err leads to pkcs7_free_message(),
which works fine on a NULL ptr.

Signed-off-by: Patrick Wildt <patrick at blueri.se>

diff --git a/lib/efi_loader/efi_variable.c b/lib/efi_loader/efi_variable.c
index 58f8fae358..c5fe896de2 100644
--- a/lib/efi_loader/efi_variable.c
+++ b/lib/efi_loader/efi_variable.c
@@ -519,9 +519,8 @@ static efi_status_t efi_variable_authenticate(u16 *variable,
 	var_sig = efi_variable_parse_signature(auth->auth_info.cert_data,
 					       auth->auth_info.hdr.dwLength
 						   - sizeof(auth->auth_info));
-	if (IS_ERR(var_sig)) {
+	if (!var_sig) {
 		debug("Parsing variable's signature failed\n");
-		var_sig = NULL;
 		goto err;
 	}