Input: iqs7222 - avoid dereferencing a NULL pointer

Input: iqs7222 - avoid dereferencing a NULL pointer

Select callers of iqs7222_parse_props() do not expect a child node
to be derived and returned via pointer. As such, these callers set
**child_node to NULL. However, this pointer is dereferenced in all
cases.

To solve this problem, dereference the pointer only for cases that
expect a child node in the first place. In these cases, the caller
provides a valid pointer.

Fixes: e505edaedcb9 ("Input: add support for Azoteq IQS7222A/B/C")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20220417214132.497487-1-jeff@labundy.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>