scsi: isci: Make local function port_state_name() static

scsi: isci: Make local function port_state_name() static

Fixes the following W=1 kernel build warning(s):

 drivers/scsi/isci/port.c:65:13: warning: no previous prototype for ‘port_state_name’ [-Wmissing-prototypes]

Link: https://lore.kernel.org/r/20210317091125.2910058-8-lee.jones@linaro.org
Cc: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>