oracleasm: Fix memory leak

oracleasm: Fix memory leak

Orabug: 28506080

As part of the ongoing changes to the block layer, the semantics of
bip_for_each_vec() changed from walking the entire bip vec (as originally
designed) to only walking the residual. This led to a memory leak as page
cache pages were not released during I/O completion.

Manually walk the bip vec in oracleasm instead of relying on the block
layer helper.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>