regulator: fix typo in Kconfig and max8973-regulator

MAX8973 is supposed to be MAX8973A. Kconfig and the
initial comment of max8973-regulator.c were modified
accordingly.

Signed-off-by: Ramona Alexandra Nechita <ramona.nechita@analog.com>
Link: https://lore.kernel.org/r/20210920061137.10884-1-ramona.nechita@analog.com


Signed-off-by: Mark Brown <broonie@kernel.org>