[AGPGART] Fix broken serverworks tlb flush routine.

[AGPGART] Fix broken serverworks tlb flush routine.
This is horribly broken due to a jiffy wrap bug, we never get out of
the while loop, preventing booting on a kernel with this driver
compiled in. (See https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=124495)

The warning message there has never been reported in any bug report
that google can find, so I'm of the opinion that this driver is trying
to be too clever for its own good.  Rip out the jiffies logic completely,
it should be totally unnecessary.