regulator: tps6507x: Fix boot regression due to testing wrong init_data pointer

A NULL init_data once incremented will lead to oops, fix it.

Fixes: f979c08f ("regulator: tps6507x: Convert to regulator core's simplified DT parsing code")
Reported-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>