STM32 Ethernet driver build failure with CONFIG_ASSERT=1

[bwasim]

Describe the bug
STM32 Ethernet driver fails to build with CONFIG_ASSERT=1. This is introduced after the changeset under #25393 which added the following code,

/* Now that the iface is setup, we are safe to enable IRQs. */
__ASSERT_NO_MSG(DEV_CFG(dev)->config_func() != NULL);
DEV_CFG(dev)->config_func();

The assertion is supposed to validate that the function call is valid while here we invoke the function and compare with its output. As the function returns VOID, we get a build error with assertion enabled. Stupidity on my part and

Expected behavior
No build failure with Ethernet+Assert enabled.

Impact
Unable to build / test Ethernet. Regression.

Screenshots or console output

In file included from ../../../../../../include/kernel_includes.h:22,
                 from ../../../../../../include/kernel.h:17,
                 from /home/buildslave/src/github.com/zephyrproject-rtos/zephyr/drivers/ethernet/eth_stm32_hal.c:12:
/home/buildslave/src/github.com/zephyrproject-rtos/zephyr/drivers/ethernet/eth_stm32_hal.c: In function 'eth_iface_init':
/home/buildslave/src/github.com/zephyrproject-rtos/zephyr/drivers/ethernet/eth_stm32_hal_priv.h:48:3: error: void value not ignored as it ought to be
   48 |  ((const struct eth_stm32_hal_dev_cfg *)(dev)->config_info)
../../../../../../include/sys/__assert.h:86:9: note: in definition of macro '__ASSERT_NO_MSG'
   86 |   if (!(test)) {                                            \
      |         ^~~~
/home/buildslave/src/github.com/zephyrproject-rtos/zephyr/drivers/ethernet/eth_stm32_hal.c:481:19: note: in expansion of macro 'DEV_CFG'
  481 |   __ASSERT_NO_MSG(DEV_CFG(dev)->config_func() != NULL);
      |                   ^~~~~~~
[48/165] Building C object zephyr/arch/arch/arm/core/aarch32/cortex_m/CMakeFiles/arch__arm__core__aarch32__cortex_m.dir/scb.c.obj

[bwasim]

cc: @erwango