wbsd: fix section mismatch warnings

This patch fixes the following section mismatch warnings

...

WARNING: vmlinux.o(.init.text+0x29d40): Section mismatch: reference to .exit.text:wbsd_release_resources (between 'wbsd_init' and 'wbsd_probe')
WARNING: vmlinux.o(.init.text+0x29d49): Section mismatch: reference to .exit.text:wbsd_free_mmc (between 'wbsd_init' and 'wbsd_probe')
WARNING: vmlinux.o(.init.text+0x29f28): Section mismatch: reference to .exit.text:wbsd_free_mmc (between 'wbsd_init' and 'wbsd_probe')

...

Signed-off-by: Gabriel Craciunescu <nix.or.die@googlemail.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>