cmp_kem.c: fix return in case of error #1117

Job	Run time
run-checker (no-cmp)	7m 22s
run-checker (no-cms)	9m 35s
run-checker (no-dgram)	7m 21s
run-checker (no-dh)	7m 9s
run-checker (no-dtls)	7m 16s
run-checker (no-ec)	6m 36s
run-checker (no-ec2m)	6m 56s
run-checker (no-ecx)	9m 25s
run-checker (no-http)	7m 20s
run-checker (no-legacy)	10m 32s
run-checker (no-sock)	9m 0s
run-checker (enable-ssl-trace)	7m 26s
run-checker (no-threads)	8m 7s
run-checker (no-thread-pool)	7m 27s
run-checker (no-default-thread-pool)	9m 15s
run-checker (no-tls)	8m 3s
run-checker (no-tls1_2)	7m 5s
run-checker (no-tls1_3)	7m 56s
run-checker (enable-trace enable-fips)	8m 7s
run-checker (no-ui)	8m 26s
run-checker (no-quic)	7m 14s
	2h 47m 38s

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