ARM: AM335x: mux: change mmc0 cd pinmux from mmc0_sdcd to gpio

Currently omap_hsmmc driver doesn't use sdcd pin to detect
whether the card is present or not. Instead the same pin is used
as GPIO to detect card presence. So change the pin mux mode from
mmc0_sdcd to gpio0_6.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>