spi: bcm2835: Micro-optimise IRQ handler

spi: bcm2835: Micro-optimise IRQ handler

The IRQ handler only needs the struct spi_controller for the sake of
the completion at the end of a transfer. Passing the struct bcm2835_spi
directly as the IRQ data allows that level of indirection to be pushed
into the completion path for the reverse lookup, and avoided entirely
in all other cases.

This saves one explicit load in the critical path, plus (for a GCC 8.3
build) two registers worth of stack frame overhead.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/6b401cb521539caffab21f05b4c8cba6c9d27c6e.1592261248.git.robin.murphy@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>