[POWERPC] Fix compile warning in pseries xics code

In 616883df78bd4b3fcdb6ddc39bd3d4cb902bfa32 request_irq was marked as
__must_check so we must... er... check it.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
1 file changed