drm/i915: Remove duplicated definition of intel_update_rawclk

A few line above we have another definition of intel_update_rawclk()
keeping that one as the function is implemented in intel_cdclk.c.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180918204714.27306-6-jose.souza@intel.com