Add symlink for Dell XPS 15 9550 Broadcom Bluetooth patch-ram file

Add symlink for Dell XPS 15 9550 Broadcom Bluetooth patch-ram file

The linux-firmware repo does not contain many Broadcom (now Cypress)
Bluetooth patch-ram files, because we have never been able to get
permission to re-distribute those.

We do have one file for the for HTC Vive, which was submitted by HTC
themselves with permission from Cypress.

That file contain a "BCM20703A1 Generic USB 20Mhz fcbga_BU" patch-ram
build. The patch-ram files used by Windows for the Bluetooth module
in the XPS 15 9550, USB-id 0a5c:6410 is also a "BCM20703A1 Generic
USB 20Mhz fcbga_BU" patch-ram build. Since the build-parameters
(crystal MHz, package/module type used) between the 2 builds are an
exact match we can also use the HTC submitted patch-ram for the
XPS 15 9550. So lets add a symlink for this.

This will make the Bluetooth on the XPS 15 9550 work out of the box,
when linux-firmware is installed, without the user needing to go and
find a suitable patch-ram file themselves.

This has been tested on a XPS 15 9550 with both Bluetooth HID and
Bluetooth audio devices.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
[Modified to use Link function in WHENCE by Josh Boyer <jwboyer@kernel.org]

Signed-off-by: Josh Boyer <jwboyer@kernel.org>