regmap: debugfs: Fix more error path regressions

Many error paths in __regmap_init rely on ret being pre-initialised to
-EINVAL, add an extra initialisation in after the new call to
regmap_set_name.

Fixes: 94cc89eb ("regmap: debugfs: Fix handling of name string for debugfs init delays")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20200918152212.22200-1-ckeepax@opensource.cirrus.com


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