FROMLIST: modpost: Make static exports fatal

Using EXPORT_SYMBOL*() on static functions is fundamentally wrong.
Modpost currently reports that as a warning, but clearly this is not a
pattern we should allow, and all in-tree occurences should have been
fixed by now. So, promote the warn() message to fatal() to make sure
this never happens again.

Bug: 174214891
Link: https://lore.kernel.org/lkml/20201124182420.2202514-1-qperret@google.com/


Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: Ic1382bfa24db556161cf1a184a4d44724d7849a1