perf probe: Fix wrong warning in __show_one_line() if read(1) errors happen

This was introduced by commit fde52dbd7f71934aba4e150f3d1d51e826a08850.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <m3y67hsr0m.fsf@gmail.com>
Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/probe-event.c

@@ -309,7 +309,7 @@ static int __show_one_line(FILE *fp, int l, bool skip, bool show_num)
 	return 1;
 error:
 	if (ferror(fp)) {
-		pr_warning("Source file is shorter than expected.\n");
+		pr_warning("File read error: %s\n", strerror(errno));
 		return -1;
 	}
 	return 0;