package/tpm2-tss: fix build on host without groupadd

Override check for groupadd as already done for setfacl since commit
d9123dd7 to avoid the following build
failure:

checking for groupadd... no
configure: error: Missing required program 'groupadd': ensure it is installed and on PATH.

Fixes:
 - http://autobuild.buildroot.org/results/5accac06abbd3980484d8e2667a5446ec5d85bc1



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