drm/i915: Make lspcon_init() static

drm/i915: Make lspcon_init() static

Make lspcon_init() static since it's no longer needed outside
the compilation unit. This was correct in Kai-Heng's lspcon
patch, but I fumbled this when applying it.

Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reported-by: kernel test robot <lkp@intel.com>
Fixes: f542d671ffce ("drm/i915: Init lspcon after HPD in intel_dp_detect()")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201002090446.21104-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>