package/open62541: force Release build

package/open62541: force Release build

Force Release build to remove -Werror and avoid the following build
failure:

/home/giuliobenetti/autobuild/run/instance-3/output-1/build/open62541-1.0/arch/network_tcp.c: At top level:
cc1: error: unrecognized command line option '-Wno-static-in-inline' [-Werror]
cc1: all warnings being treated as errors

Fixes:
 - http://autobuild.buildroot.org/results/24b429ce0ae2b33e72bb6a0f523c3906e539a4fd

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