scsi: qla2xxx: Declare the fourth ql_dump_buffer() argument const

This patch makes it clear to humans and also to the compiler that
ql_dump_buffer() does not modify the memory the @buf argument points at.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Himanshu Madhani <hmadhani@marvell.com>
Reviewed-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>