drm/i915: make transcoder_name return a string

Nicer for eDP (actually "EDP" instead of "D"), and makes future
expansion for DSI transcoders easier.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/2ac55ed584e450fe154daecb6453dff8eede5e7d.1458070700.git.jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 79eea3d..f3bcafa 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12092,7 +12092,7 @@
 	DRM_DEBUG_KMS("[CRTC:%d]%s config %p for pipe %c\n", crtc->base.base.id,
 		      context, pipe_config, pipe_name(crtc->pipe));
 
-	DRM_DEBUG_KMS("cpu_transcoder: %c\n", transcoder_name(pipe_config->cpu_transcoder));
+	DRM_DEBUG_KMS("cpu_transcoder: %s\n", transcoder_name(pipe_config->cpu_transcoder));
 	DRM_DEBUG_KMS("pipe bpp: %i, dithering: %i\n",
 		      pipe_config->pipe_bpp, pipe_config->dither);
 	DRM_DEBUG_KMS("fdi/pch: %i, lanes: %i, gmch_m: %u, gmch_n: %u, link_m: %u, link_n: %u, tu: %u\n",
@@ -16221,7 +16221,7 @@
 	}
 
 	for (i = 0; i < error->num_transcoders; i++) {
-		err_printf(m, "CPU transcoder: %c\n",
+		err_printf(m, "CPU transcoder: %s\n",
 			   transcoder_name(error->transcoder[i].cpu_transcoder));
 		err_printf(m, "  Power: %s\n",
 			   onoff(error->transcoder[i].power_domain_on));