powerpc/8xx: export 'cpm_setbrg' for modules

powerpc/8xx: export 'cpm_setbrg' for modules

Fix missing export for a loadable module build:

ERROR: modpost: "cpm_setbrg" [drivers/tty/serial/cpm_uart/cpm_uart.ko] undefined!

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
[chleroy: Changed Fixes: tag]
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210122010819.30986-1-rdunlap@infradead.org