pinctrl: qcom: Don't iterate past end of function array

Timur reports that this code crashes if nfunctions is 0. Fix the
loop iteration to only consider valid elements of the functions
array.

Reported-by: Timur Tabi <timur@codeaurora.org>
Cc: Pramod Gurav <pramod.gurav@smartplayin.com>
Cc: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: Ivan T. Ivanov <iivanov@mm-sol.com>
Cc: Andy Gross <agross@codeaurora.org>
Fixes: 32745581 "pinctrl: qcom: Add support for reset for apq8064"
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>