pinctrl: armada-37xx: Fix function name in the kernel doc

Kernel doc validator is not happy:

  .../pinctrl-armada-37xx.c:926: warning: expecting prototype for armada_37xx_fill_funcs(). Prototype was for armada_37xx_fill_func() instead

Fix this by updating function name in the kernel doc.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Gregory CLEMENT <gregory.clement@bootlin.com>