spi: spi.c: Fix comment style

Capitalize first word in comment where appropriate and add
parentheses to function names.
Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: David Jander <david@protonic.nl>
Link: https://lore.kernel.org/r/20220629142519.3985486-3-david@protonic.nlSigned-off-by: Mark Brown <broonie@kernel.org>