spi-dw-mid.c along with spi-dw.h are direct users of irqreturn.h
and nothing else is being used from interrupt.h. So, switch them
to use the former instead of latter one.

While here, move the header under #ifdef CONFIG_SPI_DW_MID_DMA
in spi-dw-mid.c.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200506153025.21441-4-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>