fwu: print a message if empty capsule checks fail

When dealing with processing of the empty capsule, the capsule gets
applied only when the checks for the empty capsule pass. Print a
message to highlight if empty capsule checks fail, and return an error
value, similar to the normal capsules.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Tested-by: Michal Simek <michal.simek@amd.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

lib/efi_loader/efi_capsule.c

@@ -564,9 +564,14 @@ static efi_status_t efi_capsule_update_firmware(
 	bool fw_accept_os;
 
 	if (IS_ENABLED(CONFIG_FWU_MULTI_BANK_UPDATE)) {
-		if (fwu_empty_capsule_checks_pass() &&
-		    fwu_empty_capsule(capsule_data))
-			return fwu_empty_capsule_process(capsule_data);
+		if (fwu_empty_capsule(capsule_data)) {
+			if (fwu_empty_capsule_checks_pass()) {
+				return fwu_empty_capsule_process(capsule_data);
+			} else {
+				log_err("FWU empty capsule checks failed. Cannot start update\n");
+				return EFI_INVALID_PARAMETER;
+			}
+		}
 
 		if (!fwu_update_checks_pass()) {
 			log_err("FWU checks failed. Cannot start update\n");