drm/i915/mst: fix intel_dp_mst_hpd_irq() indentation

Remove extra indentation.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220112110319.1172110-1-jani.nikula@intel.com