ta: crypto_perf: fix coding style issues in asymm tests

Sort out some coding style issues that are better being fixed for the
consistency of the implementation of the test TAs. No functional changes.

Fixes: 14a2b2ac ("ta: crypto_perf: add asymmetric crypto perf tests")
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@foss.st.com>