Fix nightly psk build warnings

[tmael]

This PR fixes two build warnings listed below:

server-psk-nonblocking.c: In function ‘main’:

server-psk-nonblocking.c:260:29: warning: ‘select_ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
                     else if (select_ret == TEST_TIMEOUT) {
                             ^
gcc -o server-tcp server-tcp.c -Wall -I/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/include -Os -pthread -L/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/lib -lm -lwolfssl
gcc -o server-psk server-psk.c -Wall -I/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/include -Os -pthread -L/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/lib -lm -lwolfssl
gcc -o client-psk-nonblocking client-psk-nonblocking.c -Wall -I/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/include -Os -pthread -L/var/lib/jenkins/workspace/nightly-CDT-wolfssl-examples-repo-v-1-1/install-dir/lib -lm -lwolfssl
client-psk-nonblocking.c: In function ‘main’:

client-psk-nonblocking.c:207:17: warning: ‘select_ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         else if (select_ret == TEST_TIMEOUT) {
                 ^

[kaleb-himes]

Thanks Tesfa!