power: supply: lp8788: remove an unneeded NULL check

We checked that "pdata->chg_params" is non-NULL earlier in this function
so when we add "i" to it, it's still non-NULL.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Milo Kim <milo.kim@ti.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>