regulator: tps6286x-regulator: Fix a copy & paste error

The volatile_reg function is named as tps6287x_volatile_reg by mistake
when enabing the REGCACHE_MAPLE support.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://patch.msgid.link/20250714010456.4906-1-jszhang@kernel.org


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