drm/i915: Remove pointless if-else from sdvo code

The return value is a bool so we can just return the result of
the biwise AND. The compiler will take care of the rest.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180621174658.18823-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>