drivers: smbus: stm32: implicit uint8_t pointer cast causes twister to fail

[cfriedt]

Describe the bug

The smbus_stm32.c driver contains two implicit casts from uint16_t * to uint8_t *. The implicit casts themselves are not harmful, since they mean that the underlying code uses unaligned accesses.

When the driver is built under twister, the implicit cast warning is promoted to error.

Regression

• This is a regression.

The regression was unfortunately added during the stabilization period.

Steps to reproduce

Note: testsuite was added in
#99128

1. twister -c -p nucleo_g071rb -T tests/drivers/build_all/smbus/
2. See error

Relevant log output

..drivers/smbus/smbus_stm32.c:358:32: error: initialization of 'uint8_t *' {aka 'unsigned char *'} from incompatible pointer type 'uint16_t *' {aka 'short unsigned int *'} [-Werror=incompatible-pointer-types]
  358 |                         .buf = &send_word,
      |                                ^
..drivers/smbus/smbus_stm32.c:358:32: note: (near initialization for 'messages[1].buf')
..drivers/smbus/smbus_stm32.c:363:32: error: initialization of 'uint8_t *' {aka 'unsigned char *'} from incompatible pointer type 'uint16_t *' {aka 'short unsigned int *'} [-Werror=incompatible-pointer-types]
  363 |                         .buf = recv_word,
      |                                ^~~~~~~~~

Impact

Annoyance – Minor irritation; no significant impact on usability or functionality.

Environment

• OS: any
• Toolchain: Zephyr SDK v0.17.4
• Commit SHA or Version used: v4.3.0-rc3

Additional Context

Set to low priority since it's simply not seen because we do not build the driver in CI.

Found in the context of
#99128