ARM: at91: pm: add missing put_device() call in at91_pm_sram_init()

if of_find_device_by_node() succeed, at91_pm_sram_init() doesn't have
a corresponding put_device(). Thus add a jump target to fix the exception
handling for this function implementation.

Fixes: d2e46790 ("ARM: at91: pm: use the mmio-sram pool to access SRAM")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200604123301.3905837-1-yukuai3@huawei.com