drivers: intc: irqstr: Fix uninitialized variable error

Move initialization of 'enabled' variable together with declaration.
This fixes the following compiler error:
error: 'enabled' may be used uninitialized [-Werror=maybe-uninitialized]

This is not really an error but the compiler is tricked by the
K_SPINLOCK() macro.

Fixes: https://github.com/zephyrproject-rtos/zephyr/issues/88996


Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>