pinctrl: at91: Switch to using managed clk_get

This patch switches to using managed version of clk_get and hence
removes clk_put from failure path.

CC: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
CC: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Pramod Gurav <pramod.gurav@smartplayin.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>