efi_selftest: do not use efi_free_pool()

In efi_selftest we are in EFI land. We should not use U-Boot library
functions but boot time services for memory management.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_selftest/efi_selftest_block_device.c b/lib/efi_selftest/efi_selftest_block_device.c
index 1cdd830..21409ae 100644
--- a/lib/efi_selftest/efi_selftest_block_device.c
+++ b/lib/efi_selftest/efi_selftest_block_device.c
@@ -264,7 +264,7 @@
 	}
 
 	if (image) {
-		r = efi_free_pool(image);
+		r = boottime->free_pool(image);
 		if (r != EFI_SUCCESS) {
 			efi_st_error("Failed to free image\n");
 			return EFI_ST_FAILURE;