wmbattery: Free memory allocated by strdup.

This corrects a mistake in [1] noticed by Andrew Shadura [2].

[1] http://repo.or.cz/dockapps.git/commitdiff/29e5012
[2] https://github.com/d-torrance/wmbattery/commit/9f7be30#commitcomment-12965145

wmbattery/acpi.c

@@ -226,6 +226,7 @@ int find_items(char *itemname, char infoarray[ACPI_MAXITEM][128],
 			acpi_labels[label_info]);
 		snprintf(statusarray[i], sizeof(statusarray[i]), SYSFS_PATH "/%s/%s", devices[i],
 			acpi_labels[label_status]);
+		free(devices[i]);
 	}
 
 	free(devices);