coresight: etm: perf: Make symbol 'format_attr_contextid' static

The sparse tool complains as follows:

drivers/hwtracing/coresight/coresight-etm-perf.c:61:25: warning:
 symbol 'format_attr_contextid' was not declared. Should it be static?

This symbol is not used outside of coresight-etm-perf.c, so this
commit marks it static.

Link: https://lore.kernel.org/r/20210308123250.2417947-1-weiyongjun1@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20210407160007.418053-3-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm-perf.c

@@ -58,7 +58,7 @@ static ssize_t format_attr_contextid_show(struct device *dev,
 	return sprintf(page, "config:%d\n", pid_fmt);
 }
 
-struct device_attribute format_attr_contextid =
+static struct device_attribute format_attr_contextid =
 	__ATTR(contextid, 0444, format_attr_contextid_show, NULL);
 
 static struct attribute *etm_config_formats_attr[] = {