mipi_dbi: stm32: use proper type for timeout argument

The reset function uses uint32_t as its 2nd parameter, which leads to the
following compiler warning.

zephyr/drivers/mipi_dbi/mipi_dbi_stm32_fmc.c:176:18: warning:
  initialization of 'int (*)(const struct device *, k_timeout_t)' from
  incompatible pointer type 'int (*)(const struct device *, uint32_t)'
  {aka 'int (*)(const struct device *, unsigned int)'}
  [-Wincompatible-pointer-types]
  176 |         .reset = mipi_dbi_stm32_fmc_reset,
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~

When you look at similar drivers,

/drivers/mipi_dbi/mipi_dbi_smartbond.c#L126
/drivers/mipi_dbi/mipi_dbi_nxp_lcdic.c#L561

you notice they use k_timeout_t.

So the whole fix is to correct the type.

Signed-off-by: Thorsten Spätling <thorsten.spaetling@vierling.de>