gfar: Fix modpost warning

Fix the following modpost warning:

WARNING: vmlinux.o(.init.text+0x1aa6c): Section mismatch: reference to .exit.text:gfar_mdio_exit (between 'gfar_init' and 'gfar_mdio_init')

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>