ARM: dts: am57xx-idk: Use pinctrl group from dra7-mmc-iodelay.dtsi to select pulldown

commit 18aa0f4b ("ARM: dts: am57xx-idk: Select pull down
for mmc1_clk line in default mode") modified mmc1_pins_default
pinctrl group in am57xx-idk-common.dtsi in order to change the CLK
line to PIN_INPUT_PULLDOWN. However instead of modifying the pinctrl
group, use the new pinctrl group "mmc1_pins_default_no_clk_pu" in
dra7-mmc-iodelay.dtsi added specifically to be used for CLK line without
external pull up.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>