irqchip/st: Mark st_irq_syscfg_resume() __maybe_unused

When CONFIG_PM_SLEEP is disabled, the compiler raises a warning on
st_irq_syscfg_resume:

drivers/irqchip/irq-st.c:183:12: warning: 'st_irq_syscfg_resume' defined
but not used [-Wunused-function]
static int st_irq_syscfg_resume(struct device *dev)
^~~~~~~~~~~~~~~~~~~~

Annotate the function with __maybe_unused.

Signed-off-by: Jérémy Lefaure <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: Jason Cooper <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/irqchip/irq-st.c

···
 	return st_irq_syscfg_enable(pdev);
 }
 
-static int st_irq_syscfg_resume(struct device *dev)
+static int __maybe_unused st_irq_syscfg_resume(struct device *dev)
 {
 	struct st_irq_syscfg *ddata = dev_get_drvdata(dev);