update_engine: uint64_t GetPartitionSize()

GetPartitionSize() was truncating our endOffset when the function runs
on a 32 bit device with partition size > 2^32 bytes. This resulted in
early termination of verification phase of OTA without any complaints on
update_engine side. This early termination then resulted in some cryptic
I/O requests that had led us to think there was a dm-user/snapuserd I/O
failure rather than a failure in userspace.

Bug: 361048795
Test: partial OTA of product partition on p11 device
Change-Id: Id4fb8166db09f12232f8f39f8a151b1a85cbf501
diff --git a/payload_consumer/filesystem_verifier_action.cc b/payload_consumer/filesystem_verifier_action.cc
index 2934fb7..45faebb7 100644
--- a/payload_consumer/filesystem_verifier_action.cc
+++ b/payload_consumer/filesystem_verifier_action.cc
@@ -456,7 +456,7 @@
   }
 }
 
-size_t FilesystemVerifierAction::GetPartitionSize() const {
+uint64_t FilesystemVerifierAction::GetPartitionSize() const {
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
   switch (verifier_step_) {