mfd: tps65218: Remove unused *rdev[] from struct tps65218

The *rdev[] is not used since commit 413be59e
"regulator: tps65218: Remove unnecessary regulator_unregister call".

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>