mfd: syscon: Don't free allocated name for regmap_config

The name allocated for the regmap_config structure is freed
pretty early, right after the registration of the MMIO region.

Unfortunately, that doesn't follow the life cycle that debugfs
expects, as it can access the name field long after the free
has occurred.

Move the free on the error path, and keep it forever otherwise.

Fixes: e15d7f2b ("mfd: syscon: Use a unique name with regmap_config")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>