scsi: qla4xxx: Mark symbols static where possible

We get 1 warning when build kernel with W=1:
drivers/scsi/qla4xxx/ql4_nx.c:1846:10: warning: no previous prototype for 'ql4_84xx_ipmdio_rd_reg' [-Wmissing-prototypes]

In fact, this function is only used in the file in which it is declared
and don't need a declaration, but can be made static. This patch marks
this function with 'static'.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Nilesh Javali <nilesh.javali@qlogic.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>