ACPI/nfit: avoid accessing uninitialized memory in acpi_nfit_ctl()

The ACPI_ALLOCATE() does not zero the "buf", so when the condition
"integer->type != ACPI_TYPE_INTEGER" in int_to_buf() is met, the result
is unpredictable in acpi_nfit_ctl().

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/20201118073517.1884-1-thunder.leizhen@huawei.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/core.c

@@ -282,18 +282,19 @@ static union acpi_object *pkg_to_buf(union acpi_object *pkg)
 
 static union acpi_object *int_to_buf(union acpi_object *integer)
 {
-	union acpi_object *buf = ACPI_ALLOCATE(sizeof(*buf) + 4);
+	union acpi_object *buf = NULL;
 	void *dst = NULL;
 
-	if (!buf)
-		goto err;
-
 	if (integer->type != ACPI_TYPE_INTEGER) {
 		WARN_ONCE(1, "BIOS bug, unexpected element type: %d\n",
 				integer->type);
 		goto err;
 	}
 
+	buf = ACPI_ALLOCATE(sizeof(*buf) + 4);
+	if (!buf)
+		goto err;
+
 	dst = buf + 1;
 	buf->type = ACPI_TYPE_BUFFER;
 	buf->buffer.length = 4;