cpufreq: sti: fix build warning

cpufreq: sti: fix build warning

Building this driver yields the following:

.../drivers/cpufreq/sti-cpufreq.c:215:50: warning: ‘%d’ directive output may be truncated writing between 1 and 10 bytes into a region of size 2 [-Wformat-truncation=]
  215 |         snprintf(name, MAX_PCODE_NAME_LEN, pcode%d, pcode);
      |                                                  ^~
.../drivers/cpufreq/sti-cpufreq.c:215:44: note: directive argument in the range [0, 2147483647]
  215 |         snprintf(name, MAX_PCODE_NAME_LEN, pcode%d, pcode);
      |                                            ^~~~~~~~~
.../drivers/cpufreq/sti-cpufreq.c:215:9: note: ‘snprintf’ output between 7 and 16 bytes into a destination of size 7
  215 |         snprintf(name, MAX_PCODE_NAME_LEN, pcode%d, pcode);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix the buffer size to avoid the warning at build time.

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>