regulator: tps6586x: fix build warning in debug build

When building the driver in debug mode, it generates
warning as

drivers/regulator/tps6586x-regulator.c: In function 'tps6586x_regulator_probe':
drivers/regulator/tps6586x-regulator.c:392:9: warning: 'id' is used uninitialized in this function [-Wuninitialized]

Fix this warning.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Reported-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>