Add a test for writing to a noinc register, which verifies that the
write does not touch adjacent registers. This test succeeds with [1]
applied and fails without it.

[1] 984a4afd ("regmap: prevent noinc writes from clobbering cache")
Signed-off-by: Ben Wolsieffer <ben.wolsieffer@hefring.com>
Link: https://lore.kernel.org/r/20231102203039.3069305-2-ben.wolsieffer@hefring.comSigned-off-by: Mark Brown <broonie@kernel.org>