pcmcia: omap_cf: Mark driver struct with __refdata to prevent section mismatch

As described in the added code comment, a reference to .exit.text is ok
for drivers registered via platform_driver_probe().  Make this explicit
to prevent the following section mismatch warning

    WARNING: modpost: drivers/pcmcia/omap_cf: section mismatch in reference: omap_cf_driver+0x4 (section: .data) -> omap_cf_remove (section: .exit.text)

that triggers on an omap1_defconfig + CONFIG_OMAP_CF=m build.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>