drm/i915/bios: Fix ports mask

PORT_A to PORT_F are regular integers defined in the enum port,
while for_each_port_masked requires a bit mask for the ports.

Current given mask: 0b111
Desired mask: 0b111111

I noticed this while Christoph was reporting a bug found on headless
GVT configuration which bisect blamed commit 3ae04c0c ("drm/i915/bios:
limit default outputs to ports A through F")

v2: Avoid unnecessary line continuations as pointed by CI and Christoph

Cc: Christoph Hellwig <hch@infradead.org>
Fixes: 3ae04c0c

 ("drm/i915/bios: limit default outputs to ports A through F")
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Tested-by: Christoph Hellwig <hch@infradead.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210723095225.562913-1-rodrigo.vivi@intel.com