airoha: en7523: fix SPI patch no prototype error

en7523 compilation on 6.12 fails with a no prototype warning. Fix this
by declaring max_transfer_size and transfer_one_message static.

Signed-off-by: Andrew LaMarche <andrewjlamarche@gmail.com>
Link: openwrt#20138
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

Author: andrewjlamarche

target/linux/airoha/patches-6.12/300-spi-Add-support-for-the-Airoha-EN7523-SoC-SPI-contro.patch

@@ -254,12 +254,12 @@
 +	return xfer->len;
 +}
 +
-+size_t max_transfer_size(struct spi_device *spi)
++static size_t max_transfer_size(struct spi_device *spi)
 +{
 +	return _ENSPI_MAX_XFER;
 +}
 +
-+int transfer_one_message(struct spi_controller *ctrl, struct spi_message *msg)
++static int transfer_one_message(struct spi_controller *ctrl, struct spi_message *msg)
 +{
 +	struct spi_transfer *xfer;
 +	int next_xfer_is_rx = 0;