drm/i915/psr: clean up PSR debugfs sink status error handling

Handle errors first and return early, and reduce indentation on the
happy day code path.

Cc: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230317134144.223936-3-jani.nikula@intel.com

drivers/gpu/drm/i915/display/intel_psr.c

@@ -2891,6 +2891,7 @@ static int i915_psr_sink_status_show(struct seq_file *m, void *data)
 		"reserved",
 		"sink internal error",
 	};
+	const char *str;
 	int ret;
 	u8 val;
 
@@ -2903,17 +2904,16 @@ static int i915_psr_sink_status_show(struct seq_file *m, void *data)
 		return -ENODEV;
 
 	ret = drm_dp_dpcd_readb(&intel_dp->aux, DP_PSR_STATUS, &val);
-
-	if (ret == 1) {
-		const char *str = "unknown";
+	if (ret != 1)
+		return ret < 0 ? ret : -EIO;
 
 	val &= DP_PSR_SINK_STATE_MASK;
 	if (val < ARRAY_SIZE(sink_status))
 		str = sink_status[val];
+	else
+		str = "unknown";
+
 	seq_printf(m, "Sink PSR status: 0x%x [%s]\n", val, str);
-	} else {
-		return ret;
-	}
 
 	return 0;
 }