drm/i915: Fix the static code analysis warning in debugfs

intel_dp->dsc_dpcd is defined as an array making the if check redundant.

Fixes: e845f099

 ("drm/i915/dsc: Add Per connector debugfs node for DSC support/enable")
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190109211414.15622-1-radhakrishna.sripada@intel.com