xtest: asym_perf: fix indentation issues

Fix a minor indentation issue in asym_test.c.

Fixes: bcd55831 ("xtest: add asymmetric cipher perf test")
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>