[SCSI] mpt2sas: make global symbols unique

The ioc_list global symbol is already used in 1st generation mpt
fusion drivers, so this patch makes it unique in the 2nd generation
driver.  I've checked the entire sources, and I don't see any other
global system missing the mpt2sas_xxx prefix.

Signed-off-by: Eric Moore <eric.moore@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>