pfk: fixed crash that occurred because of bio's without data

bio's without data are not relevant, bio_had_data checks this,
replaced redundant checks to call to this function.
Also, additional clean ups performed

Change-Id: I315bcf43cf3d32e78d53b818571da1f5175f8ac3
Signed-off-by: Andrey Markovytch <andreym@codeaurora.org>