efi_loader: EFI_HII_STRING_PROTOCOL.GetString()

Use u16_strsize().

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_loader/efi_hii.c b/lib/efi_loader/efi_hii.c
index 9f87e95..75ff58a 100644
--- a/lib/efi_loader/efi_hii.c
+++ b/lib/efi_loader/efi_hii.c
@@ -900,7 +900,7 @@
 
 			str = stbl->strings[string_id - 1].string;
 			if (str) {
-				len = (u16_strlen(str) + 1) * sizeof(u16);
+				len = u16_strsize(str);
 				if (*string_size < len) {
 					*string_size = len;