virt/sev-guest: Remove unnecessary free in init_crypto()

If the memory allocation for the auth tag fails, then there is no need
to free it.

Fixes: fce96cf0 ("virt: Add SEV-SNP guest driver")
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221018015425.887891-1-rafaelmendsr@gmail.com