[SCSI] advansys: Make sdtr_period_tbl a pointer

It's somewhat neater to make this a pointer to one of two tables
than initialising an array in the driver.  Also delete the unused
AscSynIndexToPeriod and rename host_init_sdtr_index to min_sdtr_index

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>