memory: da8xx-ddrctl: Remove unused 'node' variable

The variable 'node' is not used.  Remove it to silence compile warning:

    drivers/memory/da8xx-ddrctl.c: In function 'da8xx_ddrctl_probe':
    drivers/memory/da8xx-ddrctl.c:105:22: warning: variable 'node' set but not used [-Wunused-but-set-variable]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>