Fix segfault if building on macOS 12+ with deployment target <=11

[taligentx]

kIOMasterPortDefault was replaced by kIOMainPortDefault as of macOS 12 and was addressed in #11. However, this causes a segfault if building on macOS 12+ with an older deployment target (for example, GitHub CI/CD runners support macOS 13+ only).

This PR sets kIOMainPortDefault to 0:
https://developer.apple.com/documentation/iokit/kiomasterportdefault
"When specifying a primary port to IOKit functions, the NULL argument indicates "use the default". This is a synonym for NULL, if you'd rather use a named constant."

libusb also handles it this way:
https://github.com/libusb/libusb/blob/dcd30cec9a633fb59a619f5bf5f5582d794c8dff/libusb/os/darwin_usb.c#L52

/* Both kIOMasterPortDefault or kIOMainPortDefault are synonyms for 0. */
static const mach_port_t darwin_default_master_port = 0;

Tested by building SmuView on macOS 13 with a deployment target of 10.13, verified the segfault is fixed when running on a 10.13 system.