cpufreq/arm_big_little.c: Fixing non-terminated string

cpufreq/arm_big_little.c: Fixing non-terminated string

When declaring char name[9] = "cluster";

name[7] is equal to the string termination character '\0'.
But later on doing:

name[7] = cluster_id + '0';

clobbers the termination character, leaving non terminated
strings in the system and potentially causing undertermined
behavior.

By initialising name[9] to "clusterX" the 8th character is
set to '\0' and affecting the 7th character with the cluster
number doesn't overwite anything.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
[ np: The C standard says that the reminder of an initialized array of
  a known size should be initialized to zero and therefore this patch is
  unneeded, however this patch makes the intent more explicit to others
  reading the code. ]

Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>