power: supply: ab8500: Drop unnecessary NULL check after container_of

The result of container_of() operations is never NULL unless the element
is the first element of the embedded structure, which is not the case here.
The NULL check is therefore unnecessary and misleading. Remove it.

This change was made automatically with the following Coccinelle script.

@@
type t;
identifier v;
statement s;
@@

<+...
(
  t v = container_of(...);
|
  v = container_of(...);
)
  ...
  when != v
- if (\( !v \| v == NULL \) ) s
...+>

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>