package/ntpsec: fix build without stack-protector

Fix the following build failure without stack-protector raised since the
addition of the package in commit
27b8d0ba:

Checking for library ssp                 : not found
Checking for library ssp_nonshared       : not found
Checking if C compiler supports -fstack-protector-all : yes

[...]

The configuration failed
(complete log in /home/autobuild/autobuild/instance-2/output-1/build/ntpsec-1_2_2/build/config.log)

Fixes:
 - http://autobuild.buildroot.org/results/f38abc6b7f8464836231192cfe078a5b27319a8a
 - http://autobuild.buildroot.org/results/62be818e2f2eac07b4a2de6f4a8898cc4cc05b1f



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