regulator: qcom_spmi: Do not initialise static to NULL

Fix the following checkpatch error:

ERROR: do not initialise statics to NULL
+static struct regmap *saw_regmap = NULL;

Fixes: 0caecaa8 ("regulator: qcom_spmi: Add support for SAW")
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>