usb: misc: apple-mfi-fastcharge: Make power supply names unique

usb: misc: apple-mfi-fastcharge: Make power supply names unique

When multiple Apple devices are connected concurrently, the
apple-mfi-fastcharge driver fails to probe the subsequent devices with
the following error:

    sysfs: cannot create duplicate filename '/class/power_supply/apple_mfi_fastcharge'
    apple-mfi-fastcharge 5-2.4.3.3: probe of 5-2.4.3.3 failed with error -17

This happens because the driver uses a fixed power supply name
("apple_mfi_fastcharge") for all devices, causing a sysfs name
conflict when a second device is connected.

Fix this by generating unique names using the USB bus and device
number (e.g., "apple_mfi_fastcharge_5-12"). This ensures each
connected device gets a unique power supply entry in sysfs.

The change requires storing a copy of the power_supply_desc structure
in the per-device mfi_device struct, since the name pointer needs to
remain valid for the lifetime of the power supply registration.

Fixes: 249fa8217b84 ("USB: Add driver to control USB fast charge for iOS devices")
Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
Link: https://lore.kernel.org/r/20250602-apple-mfi-fastcharge-duplicate-sysfs-v1-1-5d84de34fac6@posteo.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>