drm/i915/sdvo: fix panel_type initialization

Commit 3f9ffce5

 ("drm/i915: Do panel VBT init early if the VBT
declares an explicit panel type") started using -1 as the value for
unset panel_type. It gets initialized in intel_panel_init_alloc(), but
the SDVO code never calls it.

Call intel_panel_init_alloc() to initialize the panel, including the
panel_type.

Reported-by: Tomi Leppänen <tomi@tomin.site>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/8896
Fixes: 3f9ffce5

 ("drm/i915: Do panel VBT init early if the VBT declares an explicit panel type")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: <stable@vger.kernel.org> # v6.1+
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Tested-by: Tomi Leppänen <tomi@tomin.site>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230803122706.838721-1-jani.nikula@intel.com