pinctrl: zte: fix 'functions' allocation in zx_pinctrl_build_state()
It fixes the following Smatch static check warning:
drivers/pinctrl/zte/pinctrl-zx.c:338 zx_pinctrl_build_state()
warn: passing devm_ allocated variable to kfree.
As we will be calling krealloc() on pointer 'functions', which means
kfree() will be called in there, devm_kzalloc() shouldn't be used with
the allocation in the first place. Fix the warning by calling kcalloc()
and managing the free procedure in error path on our own.