fbdev: omap2: Fix typo in tvc_probe_pdata

Assigning ddata->invert_polarity to itself is not very useful; the
context suggests that the right-hand side should have been
pdata->invert_polarity.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>