ACPI / EC: Mark the function acpi_ec_add_debugfs() as static in ec_sys.c

Mark the function acpi_ec_add_debugfs() as static in
ec_sys.c because it is not used outside this file.

This eliminates the following warning in ec_sys.c:
drivers/acpi/ec_sys.c:108:5: warning: no previous prototype for ‘acpi_ec_add_debugfs’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/ec_sys.c

···
 	.llseek = default_llseek,
 };
 
-int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
+static int acpi_ec_add_debugfs(struct acpi_ec *ec, unsigned int ec_device_count)
 {
 	struct dentry *dev_dir;
 	char name[64];