ARM: OMAP: STI STI_DR handling fixup

OMAP1 was using STI_DR instead of STI_RX_DR, which was causing problems
in the RX path. OMAP2 has a consolidated XTI_TRACESELECT, the logic for
trace clearing is the logical inverse of the OMAP1 STI_DR, so fix that
while we're at it.

Signed-off-by: Mikko K. Ylinen <mikko.k.ylinen@nokia.com>
Signed-off-by: Paul Mundt <paul.mundt@nokia.com>