efi_loader: correct check in efi_load_option_dp_join()

After assigning to *dp we must check this value and not dp.

Addresses-Coverity-ID: 501792 Control flow issues (DEADCODE)
Fixes: 58bef195f94e ("cmd: eficonfig: add support for setting fdt")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
index 348612c..65d2116 100644
--- a/lib/efi_loader/efi_helper.c
+++ b/lib/efi_loader/efi_helper.c
@@ -133,7 +133,7 @@
 
 		*dp = efi_dp_concat(tmp_dp, fdt_dp, *dp_size);
 		efi_free_pool(tmp_dp);
-		if (!dp)
+		if (!*dp)
 			return EFI_OUT_OF_RESOURCES;
 		*dp_size += efi_dp_size(fdt_dp) + sizeof(END);
 	}