mfd: stmfx: Fix error path in stmfx_chip_init

In error path, disable vdd regulator if it exists, but don't overload ret.
Because if regulator_disable() is successful, stmfx_chip_init will exit
successfully while chip init failed.

Fixes: 06252ade ("mfd: Add ST Multi-Function eXpander (STMFX) core driver")
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Link: https://lore.kernel.org/r/20230609092804.793100-1-amelie.delaunay@foss.st.com


Signed-off-by: Lee Jones <lee@kernel.org>