[SCSI] ipr: Remove unnecessary memory barriers

The ipr driver added some memory barriers in order to ensure
a PowerPC sync instruction was executed prior to sending a
command to the adapter to ensure the command block was
coherent with respect to the PCI bus's view of memory.
However, some time ago, the powerpc architecture writel
macros were changed to include the sync since most drivers
don't properly handle this. So remove these memory barriers
since they are not needed and result in executing twice
as many sync instructions, which has a significant performance
penalty.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>