drm/i915/hdcp: Fix config_stream_type() ret value

DP shim's config_stream_type considered to be succeeded when
return value of intel_dp_hdcp2_write_msg() equals to size of
message to be written, it makes config_stream_type to return
a zero success value in order to succeed the HDCP auth.

v2:
- config_stream_type() returns 0 on success. [Ram]

CC: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200303073838.25871-1-anshuman.gupta@intel.com