AZL-68849

In the Linux kernel, the following vulnerability has been resolved:

pinctrl: check the return value of pinmuxops::getfunction_name()

While the API contract in docs doesn't specify it explicitly, the generic implementation of the getfunctionname() callback from struct pinmuxops - pinmuxgenericgetfunctionname() - can fail and return NULL. This is already checked in pinmuxcheckops() so add a similar check in pinmuxfuncnameto_selector() instead of passing the returned pointer right down to strcmp() where the NULL can get dereferenced. This is normal operation when adding new pinfunctions.