spi: sprd-adi: silence an uninitialized variable warning

If of_get_property() fails then "size" is uninitialized and it leads to
a static checker warning:

    drivers/spi/spi-sprd-adi.c:288 sprd_adi_hw_init()
    error: uninitialized symbol 'size'.

We can silence the warning by re-arranging the order of these checks.
It obviously doesn't affect runtime at all.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mark Brown <broonie@kernel.org>