power: supply: act8945a_charger: fix of_irq_get() error check

of_irq_get() may return any negative error number as well as 0 on failure,
while the driver only checks for -EPROBE_DEFER, blithely continuing with
the call to devm_request_irq() -- that function expects *unsigned int*,
so would probably fail anyway when a large IRQ number resulting from a
conversion of a negative error number is passed to it... This, however,
is incorrect behavior -- error number is not IRQ number.

Check for 'irq <= 0' instead and return -ENXIO from probe if of_irq_get()
returned 0.

Fixes: a09209ac ("power: supply: act8945a_charger: Add status change update support")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>