modules: Add missing entry for __ex_table

The entry for __ex_table was missing, which may make __ex_table
become 1- or 2-byte aligned in modules.
Add the entry to ensure it gets 32-bit aligned.

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>