package/libsigrok: fix bluez5_utils dependency

Commit ab390616 wrongly added a
bluez_utils5 dependency instead of bluez5_utils

Fixes:
 - http://autobuild.buildroot.org/results/942aa07547068c9b47ce50c6dc016ee633e1a1c8



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>