[kmac] Revise SHA3 Pad FPV test to match the signal
[kmac] Revise SHA3 Pad FPV test to match the signal

Commit 663b814da revises the message interface name using from mask to
strb to make clear the term `mask` in KMAC/ SHA3 are for hardening
scheme for SCA attacks. The commit missed the revision of SHA3 Pad FPV
tb. This commit fixed it.

Signed-off-by: Eunchan Kim <cb7bc7ceb22698f298c67faa994fd9ddf3cab298@opentitan.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan