FAPI: Fix warnings unused variable. #711

Job	Run time
test-coverage	4m 49s
build-test (ubuntu-20.04, gcc)	2m 31s
scanbuild	11m 33s
build-test (ubuntu-20.04, clang)	3m 2s
coverity-test	0s
build-test (fedora-32, gcc)	4m 23s
test-fuzz	2m 22s
build-test (fedora-32, clang)	4m 24s
test-tcti-config	10m 44s
test-mbedtls (ubuntu-20.04)	2m 46s
build-test (opensuse-leap, gcc)	2m 57s
test-mbedtls (ubuntu-22.04-mbedtls-3.1)	2m 45s
build-test (opensuse-leap, clang)	4m 5s
	56m 21s

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