efi: Use 16-bit unicode strings

At present we use wide characters for unicode but this is not necessary.
Change the code to use the 'u' literal instead. This helps to fix build
warnings for sandbox on rpi.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_selftest/efi_selftest_block_device.c b/lib/efi_selftest/efi_selftest_block_device.c
index 62b3e04..60fa655 100644
--- a/lib/efi_selftest/efi_selftest_block_device.c
+++ b/lib/efi_selftest/efi_selftest_block_device.c
@@ -407,7 +407,7 @@
 	}
 
 	/* Read file */
-	ret = root->open(root, &file, L"hello.txt", EFI_FILE_MODE_READ,
+	ret = root->open(root, &file, u"hello.txt", EFI_FILE_MODE_READ,
 			 0);
 	if (ret != EFI_SUCCESS) {
 		efi_st_error("Failed to open file\n");
@@ -451,7 +451,7 @@
 
 #ifdef CONFIG_FAT_WRITE
 	/* Write file */
-	ret = root->open(root, &file, L"u-boot.txt", EFI_FILE_MODE_READ |
+	ret = root->open(root, &file, u"u-boot.txt", EFI_FILE_MODE_READ |
 			 EFI_FILE_MODE_WRITE | EFI_FILE_MODE_CREATE, 0);
 	if (ret != EFI_SUCCESS) {
 		efi_st_error("Failed to open file\n");
@@ -483,7 +483,7 @@
 
 	/* Verify file */
 	boottime->set_mem(buf, sizeof(buf), 0);
-	ret = root->open(root, &file, L"u-boot.txt", EFI_FILE_MODE_READ,
+	ret = root->open(root, &file, u"u-boot.txt", EFI_FILE_MODE_READ,
 			 0);
 	if (ret != EFI_SUCCESS) {
 		efi_st_error("Failed to open file\n");