misc: sram: remove redundant null pointer check before of_node_put

of_node_put has taken the null pinter check into account. So it is
safe to remove the duplicated check before of_node_put.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>