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.

As per unaligned-memory-access [0] "unaligned memory accesses [...]
will not work correctly on certain platforms and will cause performance
problems on others", so fix this.

Signed-off-by: Helge Deller <deller@gmx.de>
[mcgrof: added unaligned-memory-access justification]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/core-api/unaligned-memory-access.rst

 # [0]
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>