docs: driver-api: make interconnect title quieter

This makes it consistent with the other headings in the Linux driver
implementer's API guide.

Signed-off-by: Louis Taylor <louis@kragniz.eu>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/interconnect.rst

 .. SPDX-License-Identifier: GPL-2.0
 
 =====================================
-GENERIC SYSTEM INTERCONNECT SUBSYSTEM
+Generic System Interconnect Subsystem
 =====================================
 
 Introduction