ucc_geth: really fix section mismatch

Commit ed7e63a51d46e835422d89c687b8a3e419a4212a has tried to fix
section mismatch:

WARNING: vmlinux.o(.init.text+0x17278): Section mismatch: reference to
.exit.text:uec_mdio_exit (between 'ucc_geth_init' and 'uec_mdio_init')

But that mismatch still happens.

This patch actually fixing section mismatch by removing __exit from
the header file.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>