i2c: stm32f7: unmap DMA mapped buffer

commit 6aae87fe upstream.

Before each I2C transfer using DMA, the I2C buffer is DMA'pped to make
sure the memory buffer is DMA'able. This is handle in the function
`stm32_i2c_prep_dma_xfer()`.
If the transfer fails for any reason the I2C buffer must be unmap.
Use the dma_callback to factorize the code and fix this issue.

Note that the `stm32f7_i2c_dma_callback()` is now called in case of DMA
transfer success and error and that the `complete()` on the dma_complete
completion structure is done inconditionnally in case of transfer
success or error as well as the `dmaengine_terminate_async()`.
This is allowed as a `complete()` in case transfer error has no effect
as well as a `dmaengine_terminate_async()` on a transfer success.

Also fix the unneeded cast and remove not more needed variables.

Fixes: 7ecc8cfd ("i2c: i2c-stm32f7: Add DMA support")
Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
Cc: <stable@vger.kernel.org> # v4.18+
Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250704-i2c-upstream-v4-2-84a095a2c728@foss.st.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>