drm/i915/dp: Remove redundant sleep after AUX transaction length check.

The core already takes care of the delay before retrying. The delay now
changes to (500, 600)us instead of (500 + 1000, 600 + 1500)us.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180223221520.18464-5-dhinakaran.pandiyan@intel.com