regmap: rbtree: Fixed node range check on sync

A node starting before the minimum register is no reason to reject it,
since its end could be in range. The check for the end already exists
two lines lower, so we can just remove the incorrect check.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Mark Brown <broonie@linaro.org>