[avb] Remove redundant unsafe for get_preloaded_partition

Test: m pvmfw_img && atest libpvmfw_avb.test
Change-Id: I09ce3ea25b81048350aa5721b675421673c68a9a
diff --git a/pvmfw/avb/src/verify.rs b/pvmfw/avb/src/verify.rs
index fb18626..437f8e2 100644
--- a/pvmfw/avb/src/verify.rs
+++ b/pvmfw/avb/src/verify.rs
@@ -22,7 +22,7 @@
     slice,
 };
 
-static NULL_BYTE: &[u8] = b"\0";
+const NULL_BYTE: &[u8] = b"\0";
 
 enum AvbIOError {
     /// AVB_IO_RESULT_ERROR_OOM,
@@ -78,7 +78,7 @@
     AvbIOResult::AVB_IO_RESULT_OK
 }
 
-unsafe extern "C" fn get_preloaded_partition(
+extern "C" fn get_preloaded_partition(
     ops: *mut AvbOps,
     partition: *const c_char,
     num_bytes: usize,