spi: *: Call the dedicated transfer completion function.

[Vincent Pelletier]

Hello,

I started this fix on bcm2835.c and, because of its simplicity, thought
I should check other controllers as well.
This patch set should fix all occurrences, as of v5.11-rc2, of an SPI
controller driver calling
  complete(&...->xfer_completion);
when it could call
  spi_finalize_current_transfer(...);
as requested in Documentation/spi/spi-summary.rst .

While I did build all modified files, and these should be trivial to
check for correctness, I have not exercised all codepaths.
I have exercised spi-bcm2835 IRQ and DMA tx, but I am still hunting
for another issue which causes completion timeouts at spi/spi.c level
which seem to affect spi-bcm2835 dma transfers (both before and after
this patch set).

Regards,
Vincent Pelletier