Revert^2 "Upgrade zerocopy to 0.7.5"

893738e5702b1f065826d9a31cef2122a502da66

Change-Id: Ib91e64e7a32e6b31fa0bde93dbfc411c60d33301
diff --git a/pvmfw/src/gpt.rs b/pvmfw/src/gpt.rs
index 06bf994..71eb569 100644
--- a/pvmfw/src/gpt.rs
+++ b/pvmfw/src/gpt.rs
@@ -26,6 +26,7 @@
 use vmbase::util::ceiling_div;
 use vmbase::virtio::{pci, HalImpl};
 use zerocopy::FromBytes;
+use zerocopy::FromZeroes;
 
 type VirtIOBlk = pci::VirtIOBlk<HalImpl>;
 
@@ -156,7 +157,7 @@
 type Lba = u64;
 
 /// Structure as defined in release 2.10 of the UEFI Specification (5.3.2 GPT Header).
-#[derive(FromBytes)]
+#[derive(FromZeroes, FromBytes)]
 #[repr(C, packed)]
 struct Header {
     signature: u64,