proc: fixup test for read

/proc/kmsg can and will block if read under root.

---

 tools/testing/selftests/proc/read.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -54,7 +54,8 @@ static void f_reg(DIR *d, const char *filename)
 	int fd;
 	ssize_t rv;
 
-	fd = openat(dirfd(d), filename, O_RDONLY);
+	/* read from /proc/kmsg can block */
+	fd = openat(dirfd(d), filename, O_RDONLY|O_NONBLOCK);
 	if (fd == -1)
 		return;
 	rv = read(fd, buf, sizeof(buf));

This fixes proc-shotgun-test-read-readdir-readlink-a-little-write.patch. It helps to point that out, so that reviewers won't be scrambling around asking wtf.