powerpc: 8xx: fix a return value error in mpc8xx_pic_init

powerpc: 8xx: fix a return value error in mpc8xx_pic_init

mpc8xx_pic_init() should return -ENOMEM instead of 0 when
irq_domain_add_linear() return NULL. This cause mpc8xx_pics_init to continue
executing even if mpc8xx_pic_host is NULL.

Fixes: cc76404feaed ("powerpc/8xx: Fix possible device node reference leak")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220223070223.26845-1-hbh25y@gmail.com