mfd: stmfx: Fix stmfx_irq_init error path

In case the interrupt signal can't be configured, IRQ domain needs to be
removed.

Fixes: 06252ade ("mfd: Add ST Multi-Function eXpander (STMFX) core driver")
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>