efivars: Fix check for CONFIG_EFI_VARS_PSTORE_DEFAULT_DISABLE

The 'CONFIG_' prefix is not implicit in IS_ENABLED().
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Seth Forshee <seth.forshee@canonical.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

drivers/firmware/efivars.c

@@ -104,7 +104,7 @@ MODULE_VERSION(EFIVARS_VERSION);
 #define GUID_LEN 36
 
 static bool efivars_pstore_disable =
-	IS_ENABLED(EFI_VARS_PSTORE_DEFAULT_DISABLE);
+	IS_ENABLED(CONFIG_EFI_VARS_PSTORE_DEFAULT_DISABLE);
 
 module_param_named(pstore_disable, efivars_pstore_disable, bool, 0644);