package/collectd: fix build with dpdk_telemetry

Fix typo added by 44e0b601

Fixes:
 - http://autobuild.buildroot.org/results/770293a007d683cb6f82f1fd3bcc20967e2b4bed



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>