iscsi_ibft: iscsi_ibft_find unused variable i

int i is only needed if CONFIG_ACPI is set
so move it within a new ifdef so kernels without ACPI
don't allocate space for nothing. Fixes warning too.

Signed-off-by: Connor Hansen <cmdkhh@gmail.com>
Signed-off-by: Peter Jones <pjones@redhat.com>
[v2: Fixed warning when CONFIG_ACPI was defined]
Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>