powerpc/44x/fsp2: add missing of_node_put

Early exits from for_each_compatible_node() should decrement the
node reference counter.  Reported by Coccinelle:

./arch/powerpc/platforms/44x/fsp2.c:206:1-25: WARNING: Function
"for_each_compatible_node" should have of_node_put() before return
around line 218.

Fixes: 7813043e ("powerpc/44x/fsp2: Add irq error handlers")
Signed-off-by: Bixuan Cui <cuibixuan@linux.alibaba.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1635406102-88719-1-git-send-email-cuibixuan@linux.alibaba.com