spi: airoha: set custom sector size equal to flash page size

spi: airoha: set custom sector size equal to flash page size

Set custom sector size equal to flash page size including oob. Thus we
will always read a single sector. The maximum custom sector size is
8187, so all possible flash sector sizes are supported.

This patch is a necessary step to avoid reading flash page settings
from SNFI registers during driver startup.

Signed-off-by: Mikhail Kshevetskiy <mikhail.kshevetskiy@iopsys.eu>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patch.msgid.link/20251012121707.2296160-12-mikhail.kshevetskiy@iopsys.eu
Signed-off-by: Mark Brown <broonie@kernel.org>