clk: ux500: fix mismatched types

As reported by Rob Herring[1] there were some mismatched types between
drivers/clk/ux500/clk.h and the corresponding function definitions:

drivers/clk/ux500/clk-prcc.c:145:13: error: conflicting types for 'clk_reg_prcc_pclk'
drivers/clk/ux500/clk-prcc.c:155:13: error: conflicting types for 'clk_reg_prcc_kclk'

[1] http://article.gmane.org/gmane.linux.ports.arm.kernel/232246

Signed-off-by: Mike Turquette <mturquette@linaro.org>
Cc: Rob Herring <robherring2@gmail.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Linus Walleij <linus.walleij@linaro.org>