ARM: OMAP: dmtimer.c omap1 register fix

When I went to use dmtimer7 it did not seem to work.  I noticed that
the base addresses for dmtimers 7 and 8 were set wrong.  A simple patch
to correct a small error.  Confirmed to fix the problem on an OSK.

Signed-off-by: Matthew Percival <matthew@capgo.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>