[SCSI] aacraid: remove duplicate io callback code

Received from Mark Salyzyn from Adaptec:

This patch removes the duplicate code in the write_callback command
completion handler, and renames read_callback to io_callback. Optimized
the lba calculation into the debug print routine macro to optimize the
i/o code path.

Signed-off-by: Mark Haverkamp <markh@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>