Fix typo cpu6 -> cpu7

This prevented perfetto from clearing the ftrace buffer for cpu7
(and only cpu7). Seems a copy paste error.

Test: Untested.
Bug: 122609457
Change-Id: I2096dc333880d94cb25ba5ce50272444e8ae999e
diff --git a/cmds/atrace/atrace.rc b/cmds/atrace/atrace.rc
index 4459cef..dcb4bf7 100644
--- a/cmds/atrace/atrace.rc
+++ b/cmds/atrace/atrace.rc
@@ -163,7 +163,7 @@
     chmod 0666 /sys/kernel/tracing/per_cpu/cpu5/trace
     chmod 0666 /sys/kernel/debug/tracing/per_cpu/cpu6/trace
     chmod 0666 /sys/kernel/tracing/per_cpu/cpu6/trace
-    chmod 0666 /sys/kernel/debug/tracing/per_cpu/cpu6/trace
+    chmod 0666 /sys/kernel/debug/tracing/per_cpu/cpu7/trace
     chmod 0666 /sys/kernel/tracing/per_cpu/cpu7/trace
     chmod 0666 /sys/kernel/debug/tracing/per_cpu/cpu8/trace
     chmod 0666 /sys/kernel/tracing/per_cpu/cpu8/trace