Fixed typo in SimpleDram.

Fixing a type in SimpleDRAM.issueRequest narrows the accuracy gap
considerably. The remaining discrepancy is probably in
SimpleDram.bestRequest and will be fixed shortly.
Fixed SimpleDram.

Fixed the remaining timing discrepancies between Prismriver and
Nijikawa (there is still a discrepancy of 4 instructions, but this is
probably due to a difference in when SimpleDram receives a tick.

The conclusion: Prismriver executes the benchmark in about 6.1 seconds
on average, while Nijikawa executes the benchmark in about 16 seconds on
average, a slowdown of about 262%.