video: fbdev: atmel_lcdfb: fix return error code in atmel_lcdfb_of_init()

If devm_kzalloc() failed after the first time, atmel_lcdfb_of_init()
can't return -ENOMEM, fix this by putting the error code in loop.

Fixes: b985172b

 ("video: atmel_lcdfb: add device tree suport")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201117061350.3453742-1-yangyingliang@huawei.com