[efi] Ignore failures when attempting to install SNP HII protocol

HII seems to fail on several systems.  Since it is non-essential,
treat HII problems as non-fatal.

Debugged-by: Curtis Larsen <larsen@dixie.edu>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/interface/efi/efi_snp.c

 	if ( ( rc = efi_snp_hii_install ( snpdev ) ) != 0 ) {
 		DBGC ( snpdev, "SNPDEV %p could not install HII: %s\n",
 		       snpdev, strerror ( rc ) );
-		goto err_hii_install;
+		/* HII fails on several platforms.  It's
+		 * non-essential, so treat this as a non-fatal
+		 * error.
+		 */
 	}
 
 	/* Add to list of SNP devices */
 	       efi_devpath_text ( &snpdev->path ) );
 	return 0;
 
-	efi_snp_hii_uninstall ( snpdev );
- err_hii_install:
+	if ( snpdev->package_list )
+		efi_snp_hii_uninstall ( snpdev );
 	efidev_child_del ( efidev, snpdev->handle );
  err_efidev_child_add:
 	bs->UninstallMultipleProtocolInterfaces (
 	}
 
 	/* Uninstall the SNP */
-	efi_snp_hii_uninstall ( snpdev );
+	if ( snpdev->package_list )
+		efi_snp_hii_uninstall ( snpdev );
 	efidev_child_del ( snpdev->efidev, snpdev->handle );
 	list_del ( &snpdev->list );
 	bs->UninstallMultipleProtocolInterfaces (

src/interface/efi/efi_snp_hii.c

 	int rc;
 
 	/* Do nothing if HII database protocol is not supported */
-	if ( ! efihii )
-		return 0;
+	if ( ! efihii ) {
+		rc = -ENOTSUP;
+		goto err_no_hii;
+	}
 
 	/* Initialise HII protocol */
 	memcpy ( &snpdev->hii, &efi_snp_device_hii, sizeof ( snpdev->hii ) );
 	free ( snpdev->package_list );
 	snpdev->package_list = NULL;
  err_build_package_list:
+ err_no_hii:
 	return rc;
 }