serial: 8250_ni: Fix build warning

serial: 8250_ni: Fix build warning

Allocate memory on heap instead of stack to fix following warning that
clang version 20.1.2 produces on W=1 build.

drivers/tty/serial/8250/8250_ni.c:277:12: warning: stack frame size (1072) exceeds limit (1024) in 'ni16550_probe' [-Wframe-larger-than]
  277 | static int ni16550_probe(struct platform_device *pdev)
      |            ^
  1 warning generated.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202507030557.vIewJJQO-lkp@intel.com/
Cc: Jason Smith <jason.smith@emerson.com>
Cc: Gratian Crisan <gratian.crisan@emerson.com>
Signed-off-by: Chaitanya Vadrevu <chaitanya.vadrevu@emerson.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250711200418.1858682-2-chaitanya.vadrevu@emerson.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>