mpt3sas: Fix warnings exposed by W=1

Trivial non-functional changes for a couple annoying things:

  1) Functions local to files are not declared static, which is
  frustrating when reading the code because it's non-obvious at first
  glance what's actually called from other files.

  2) Set-but-unused variables abound, presumably to mask -Wunused-result
  errors in the past. None of these are flagged today though (with one
  exception noted below), so remove them.

Fixing (2) exposed the fact that we improperly ignore the return value
of scsi_device_reprobe() in _scsih_reprobe_lun(). Fixing the calling
code to deal with the potential error is non-trivial, so for now just
WARN().

Signed-off-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Chaitra P B <chaitra.basappa@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>