If you read the Kernel COPYING file, it is explicitly said there that the Kernel
is licensing with GPLv2. The _ONLY_ exception there is the allowance to use
the kernel via normal syscalls:
"NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".
Also note that the GPL below is copyrighted by the Free Software
Foundation, but the instance of code that it refers to (the Linux
kernel) is copyrighted by me and others who actually wrote it."
The usage of EXPORT_SYMBOL() is not covered there, so those symbols are also
covered by GPLv2.
As the usage of a kernel symbol by a proprietary driver is not explicitly
listed there as a GPLv2 exception, the only concrete results of this patch is
to spread FUD, as EXPORT_SYMBOL might generate some doubts on people that
don't read the Kernel's COPYING file.
With or without this patch, anyone with intelectual rights in the Kernel may
go to court to warrant their rights against the infringing closed source drivers.
By not making it explicitly, you're only trying to fool people that using
it might be allowed.