gpio: mlxbf2: Use DEFINE_RES_MEM_NAMED() helper macro

Use DEFINE_RES_MEM_NAMED() to save a couple of lines of code, which makes
the code a bit shorter and easier to read.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Asmaa Mnebhi <asmaa@nvidia.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>