patch 8.1.1032: warnings from clang static analyzer

Problem:    Warnings from clang static analyzer. (Yegappan Lakshmanan)
Solution:   Fix relevant warnings.
diff --git a/src/os_unix.c b/src/os_unix.c
index 47b27cf..0d9f69e 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -6147,9 +6147,9 @@
 	}
 # endif
 #ifdef FEAT_JOB_CHANNEL
-	/* also call when ret == 0, we may be polling a keep-open channel */
+	// also call when ret == 0, we may be polling a keep-open channel
 	if (ret >= 0)
-	    ret = channel_poll_check(ret, &fds);
+	    channel_poll_check(ret, &fds);
 #endif
 
 #else /* HAVE_SELECT */