video: fbdev: vermilion: use 64-bit arithmetic instead of 32-bit

Cast _pitch_ to u64 in order to give the compiler complete information
about the proper arithmetic to use. Notice that this variable is
being used in a context that expects an expression of type u64
(64 bits, unsigned).

The expression pitch * var->yres_virtual is currently being evaluated
using 32-bit arithmetic and the result of the operation is being stored
into variable mem, which is a variable of type u64. Based on that,
chances are there is a potential integer overflow as a result of the
operation.

Addresses-Coverity-ID: 200655 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/vermilion/vermilion.c

@@ -651,7 +651,7 @@ static int vmlfb_check_var_locked(struct fb_var_screeninfo *var,
 	}
 
 	pitch = ALIGN((var->xres * var->bits_per_pixel) >> 3, 0x40);
-	mem = pitch * var->yres_virtual;
+	mem = (u64)pitch * var->yres_virtual;
 	if (mem > vinfo->vram_contig_size) {
 		return -ENOMEM;
 	}