efi_loader: variable: fix secure state initialization

Under the new file-based variable implementation, the secure state
is always and falsely set to 0 (hence, the secure boot gets disabled)
after the reboot even if PK (and other signature database) has already
been enrolled in the previous boot.

This is because the secure state is set up *before* loading non-volatile
variables' values from saved data.

This patch fixes the order of variable initialization and secure state
initialization.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Fixes: 5f7dcf07 ("efi_loader: UEFI variable persistence")