pinctrl: mediatek: make devm allocations safer and clearer in mtk_eint_do_init()

mtk_eint_do_init() allocates several pointer arrays which are then
populated in a per-instance loop and freed on error. The arrays are
currently allocated with devm_kmalloc(), so their entries are left
uninitialised until the per-instance allocations succeed.

On a failure in the middle of the loop, the error path iterates over
the full nbase range and calls devm_kfree() on each element. For
indices which were never initialised, the corresponding array entries
contain stack garbage. If any of those happen to be non-zero,
devm_kfree() will pass them to devres_destroy(), which will WARN
because there is no matching devm_kmalloc() resource for such bogus
pointers.

Improve the robustness and readability by:

- Using devm_kcalloc() for the pointer arrays so that all entries
start as NULL, ensuring that only genuinely initialised elements
may be freed and preventing spurious WARN_ON()s in the error path.
- Switching the allocations to sizeof(*ptr) / sizeof(**ptr) forms,
avoiding hard-coded element types and making the code more resilient
to future type changes.
- Dropping the redundant NULL checks before devm_kfree(), as
devm_kfree() safely handles NULL pointers.

The functional behaviour in the successful initialisation path remains
unchanged, while the error handling becomes simpler and less
error-prone.

Reviewed-by: fanggeng <fanggeng@lixiang.com>
Signed-off-by: Liang Jie <liangjie@lixiang.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>