drivers: intc: irqstr: initialize 'enabled' variable

Initialize the 'enabled' variable before using it.
This fixes the following compilation warning:

"warning: 'enabled' may be used uninitialized [-Wmaybe-uninitialized]"

issued when compiling with `CONFIG_DEBUG` enabled.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>
Tested-by: Daniel Baluta <daniel.baluta@nxp.com>