sysapi: Initialize variable to 0
sysapi: Initialize variable to 0

Clang complains that "tag" might be used uninitialized:
"error: variable 'tag' is used uninitialized whenever 'if' condition is true"
Fixing it by initializing to 0.

Signed-off-by: Peter Huewe <014f16385c5a8ff1646b588a3d5169b595c0f10e@gmx.de>

tpm2-software/tpm2-tss,01org/tpm2-tss,01org/TPM2.0-TSS,01org/TPM2.0-TSS,01org/TPM2.0-TSS,01org/TPM2.0-TSS,tpm2-software/tpm2-tss,01org/tpm2-tss,01org/tpm2-tss,tpm2-software/tpm2-tss