stm32cube: stm32h7: eth: Fix calculation of the tail pointer

Cherry-picking commit ceda3ceeca2ee77a76d2de2ee6b560ad87c90a48
in STM32H7 Cube HAL
https://github.com/STMicroelectronics/stm32h7xx-hal-driver/



Fixed in hal_stm32 main branch following cube version update
from version v1.11.2 to version v1.12.0.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>