lib: sbi: sse: remove superfluous sbi_list_empty() check

The list loop below that check is actually not looping if the list is
empty so there was no need for this check.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reported-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>