nvmem: sunxi_sid: remove unused variable in probe

This patch fixes below warning:
sunxi_sid.c:157:6: warning: unused variable 'ret' [-Wunused-variable]

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>