microblaze: Fix typo in exception.c

Trivial fix.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/c4ede6dc738c5bd7c518f3bb2c9410b15c102e20.1655299267.git.michal.simek@amd.com
1 file changed