staging: mt7621-pinctrl: Use correct pointer type argument for sizeof

Fix the following coccicheck warning:

drivers/staging/mt7621-pinctrl/pinctrl-rt2880.c:223:14-36: WARNING: Use
correct pointer type argument for sizeof
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200420133416.3087-1-yanaijie@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-pinctrl/pinctrl-rt2880.c

@@ -220,7 +220,7 @@ static int rt2880_pinmux_index(struct rt2880_priv *p)
 	/* allocate our function and group mapping index buffers */
 	f = p->func = devm_kcalloc(p->dev,
 				   p->func_count,
-				   sizeof(struct rt2880_pmx_func),
+				   sizeof(*p->func),
 				   GFP_KERNEL);
 	gpio_func.groups = devm_kcalloc(p->dev, p->group_count, sizeof(int),
 					GFP_KERNEL);