board: libre-computer: check interface before comparing it in set_dfu_alt_info()

board: libre-computer: check interface before comparing it in set_dfu_alt_info()

When set_dfu_alt_info() is called, interface can be NULL when called for
the EFI capsule, so check it before calling it with strcmp().

Fixes: 12ea40d29dc ("ARM: meson: add support for Libre Computer aml-s905d3-cc")
Fixes: 9e6e6b034b1 ("ARM: meson: add support for Libre Computer aml-a311d-cc")
Fixes: 75c87c6cbc0 ("board: libre-computer: aml-s805x-cc: Enable capsule updates")
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Link: https://lore.kernel.org/r/20250403-u-boot-fix-set-dfu-alt-info-interface-v1-1-1fdd12463186@linaro.org
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>