LU-13814 clio: rename pvec to cdp

LU-13814 clio: rename pvec to cdp

Pvec is an older naming convention that sort of matches a
convention used in the kernel, but is really starting to
feel odd as a local variable name for cl_dio_pages.

Rename accordingly.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <patrick.farrell@oracle.com>
Change-Id: I375b80e4e50dcb2aa7c640df32a8fe896e5fc082
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52492
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>