libsnapshot: Fix incorrect CHECK in PerformInitTransition().

The sector count can decrease as the merge progresses, so we only care
that the sector count is less than or equal to the device size.

Bug: N/A
Test: reboot during VABC merge
Change-Id: I1da956456ea28ca0fdfbf9373848987c9f71ff68
diff --git a/fs_mgr/libsnapshot/snapshot.cpp b/fs_mgr/libsnapshot/snapshot.cpp
index 6570044..21b720e 100644
--- a/fs_mgr/libsnapshot/snapshot.cpp
+++ b/fs_mgr/libsnapshot/snapshot.cpp
@@ -1410,7 +1410,7 @@
             return false;
         }
 
-        CHECK(base_sectors == target.spec.length);
+        CHECK(base_sectors <= target.spec.length);
 
         if (!snapuserd_client_->AttachDmUser(misc_name)) {
             // This error is unrecoverable. We cannot proceed because reads to