drm/dp: add missing ')' to I2C nack debug message

 "(an unmatched left parenthesis
  creates an unresolved tension
  that will stay with you all day."
               -- Randall Munroe

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180727203331.27778-1-paulo.r.zanoni@intel.com