serdev: Fix detection of UART devices on Apple machines.

serdev: Fix detection of UART devices on Apple machines.

On Apple devices the _CRS method returns an empty resource template, and
the resource settings are instead provided by the _DSM method. But
commit fb668f696db3d9cc65723c1f3d5352e4f2cd8a33 (serdev: Add ACPI
devices by ResourceSource field) changed the search for serdev devices
to require valid, non-empty resource template, thereby breaking Apple
devices and causing bluetooth devices to not be found.

This expands the check so that if we don't find a valid template, and
we're on an Apple machine, then just check for the device being an
immediate child of the controller and having a "baud" property.

Cc: <stable@vger.kernel.org> # 5.5
Fixes: fb668f696db3 ("serdev: Add ACPI devices by ResourceSource field")
Signed-off-by: Ronald Tschalär <ronald@innovation.ch>
Link: https://lore.kernel.org/r/20200211194723.486217-1-ronald@innovation.ch
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>