releasetools: Fix the wrong command when falling back to bsdiff.

Commit b937ead5 added the fallback to
bsdiff on imgdiff failures. However, it missed setting the transfer
style accordingly, which led to patch header mismatch.

Bug: 68659848
Test: Generate an incremental that has the fallback from imgdiff to
      bsdiff. Examine the generated transfer list and verify that it has
      "bsdiff" for the fallback command.

Change-Id: I55e46879d590a8af82ea796b9d98ffdb30360408