aperf: fail early if user may not access MSR.

Based on a suggestion by Thomas Renninger.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
diff --git a/utils/aperf.c b/utils/aperf.c
index 893e8eb..063f4a4 100644
--- a/utils/aperf.c
+++ b/utils/aperf.c
@@ -403,7 +403,7 @@
 		return EXIT_FAILURE;
 	}
 
-	ret = access(msr_path, F_OK);
+	ret = access(msr_path, R_OK);
 	if (ret < 0) {
 		fprintf(stderr, "Error reading %s, load/enable msr.ko\n", msr_path);
 		goto out;