drm/i915/dsi: Fix comment typo

Change 'befor' to 'before'.

Signed-off-by: zuoqilin <zuoqilin@yulong.com>
[Jani: Fix comment marker placement while applying.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210317074228.1147-1-zuoqilin1@163.com