dir: Add printf format checks to log

dir: Add printf format checks to log

salvage.c uses the Log() function defined by vol/common.c. At the
moment, this isn't defined in a way that we can easily grab its prototype,
so the code has an extern definition at the beginning. For now, just add
format checks to this definition.

Fix all of the fallout from this - we were casting to intptr, and
printing with %x - use AFS_PTR_FMT as nature intended.

Change-Id: I2110ebddbe207c307fcad00ab89e5818824a644d
Reviewed-on: http://gerrit.openafs.org/2446
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>