of: property: Avoiding using uninitialized variable @imaplen in parse_interrupt_map()

parse_interrupt_map() will use uninitialized variable @imaplen if fails
to get property 'interrupt-map'.

Fix by using the variable after successfully getting the property.

Fixes: e7985f43 ("of: property: Fix fw_devlink handling of interrupt-map")
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20250109-of_core_fix-v4-6-db8a72415b8c@quicinc.com


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>