powerpc: Fix spelling mistake "mesages" -> "messages" in Kconfig

There is a spelling mistake in the Kconfig text. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210704093846.36972-1-colin.king@canonical.com