ACPI: fix NULL pointer dereference

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

ACPI: fix NULL pointer dereference

Commit 71f642833284 ("ACPI: utils: Fix reference counting in

for_each_acpi_dev_match()") started doing "acpi_dev_put()" on a pointer

that was possibly NULL. That fails miserably, because that helper

inline function is not set up to handle that case.

Just make acpi_dev_put() silently accept a NULL pointer, rather than

calling down to put_device() with an invalid offset off that NULL

pointer.