mmc: Staticize sd_select_bus_width

Staticize the function since it's only used in mmc.c .

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Tom Rini <trini@konsulko.com>

drivers/mmc/mmc.c

@@ -1334,7 +1334,7 @@ static int sd_set_card_speed(struct mmc *mmc, enum bus_mode mode)
 	return 0;
 }
 
-int sd_select_bus_width(struct mmc *mmc, int w)
+static int sd_select_bus_width(struct mmc *mmc, int w)
 {
 	int err;
 	struct mmc_cmd cmd;