drm/i915/tgl: Fix missing parentheses on TGL_TRANS_DDI_FUNC_CTL_VAL_TO_PORT

In this case we want to apply the mask and then shift so the
parentheses is needed.

SPANK! SPANK! SPANK! Naughty programmer!

Fixes: 9749a5b6

 ("drm/i915/tgl: Fix the read of the DDI that transcoder is attached to")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190812175405.14479-1-jose.souza@intel.com