drivers: ethernet: eth_stm32_hal: Fix cppcheck warning

When running cppcheck on eth_stm32_hal.c it generated a warning for
shiftTooManyBitsSigned.

The solution is to make sure that the numeric value shifted is unsigned.

Updated to use BIT() macro as suggested by GeorgeGCV.

Fixes: #57336

Signed-off-by: Stefan Petersen <spe@ciellt.se>