mfd: intel_quark_i2c_gpio: Don't play dirty trick with const

As Linus rightfully noticed, the driver plays dirty trick with const,
i.e. it assigns a place holder data structure to the const field
in the MFD cell and then drops the const by explicit casting. This is
not how it should be.

Assign local pointers of the cell and resource to the respective
non-const place holders in the intel_quark_i2c_setup() and
intel_quark_gpio_setup().

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>