staging: fbtft: Use devm_kcalloc instead of devm_kzalloc

Replace devm_kzalloc with devm_kcalloc to ensure there are no integer
overflows from the multiplication of a number * sizeof

The following Coccinelle semantic patch was used to make this change:
//<smpl>
@@
expression dev,E1,E2,E3,E4;
@@

- devm_kzalloc(dev,E1*E2*sizeof(E3),E4)
+ devm_kcalloc(dev,E1*E2,sizeof(E3),E4)
//</smpl>
Signed-off-by: NAmitoj Kaur Chawla <amitoj1606@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-core.c

@@ -736,8 +736,11 @@ struct fb_info *fbtft_framebuffer_alloc(struct fbtft_display *display,
 		goto alloc_fail;
 
 	if (display->gamma_num && display->gamma_len) {
-		gamma_curves = devm_kzalloc(dev, display->gamma_num * display->gamma_len * sizeof(gamma_curves[0]),
-						GFP_KERNEL);
+		gamma_curves = devm_kcalloc(dev,
+					    display->gamma_num *
+					    display->gamma_len,
+					    sizeof(gamma_curves[0]),
+					    GFP_KERNEL);
 		if (!gamma_curves)
 			goto alloc_fail;
 	}