spi: airoha: fix airoha_snand_{write,read}_data data_len estimation

spi: airoha: fix airoha_snand_{write,read}_data data_len estimation

Fix data length written and read in airoha_snand_write_data and
airoha_snand_read_data routines respectively if it is bigger than
SPI_MAX_TRANSFER_SIZE.

Fixes: a403997c1201 ("spi: airoha: add SPI-NAND Flash controller driver")
Tested-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20240913-airoha-spi-fixes-v1-2-de2e74ed4664@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>