rtc: mcp795: Add SPI ID table

Currently autoloading for SPI devices does not use the DT ID table, it uses
SPI modalises. Supporting OF modalises is going to be difficult if not
impractical, an attempt was made but has been reverted, so ensure that
module autoloading works for this driver by adding an id_table listing the
SPI IDs for everything.

Fixes: 96c8395e ("spi: Revert modalias changes")
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210927130240.33693-1-broonie@kernel.org