[SCSI] mpt2sas: Removed compiler warnnings when logging is disabled

The compiler throws warning messages while compiling without
CONFIG_SCSI_MPT2SAS_LOGGING.
Set proper ifdef for CONFIG_SCSI_MPT2SAS_LOGGING to avoid warnnings.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>