[media] pms: Fix a bad usage of the stack

As warned by smatch:
	drivers/media/parport/pms.c:632:21: warning: Variable length array is used.

The pms driver is doing something really bad: it is using the
stack to read data into a buffer whose size is given by the
user by the read() syscall. Replace it by a dynamically allocated
buffer.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/parport/pms.c

@@ -629,11 +629,15 @@ static int pms_capture(struct pms *dev, char __user *buf, int rgb555, int count)
 {
 	int y;
 	int dw = 2 * dev->width;
-	char tmp[dw + 32]; /* using a temp buffer is faster than direct  */
+	char *tmp; /* using a temp buffer is faster than direct  */
 	int cnt = 0;
 	int len = 0;
 	unsigned char r8 = 0x5;  /* value for reg8  */
 
+	tmp = kmalloc(dw + 32, GFP_KERNEL);
+	if (!tmp)
+		return 0;
+
 	if (rgb555)
 		r8 |= 0x20; /* else use untranslated rgb = 565 */
 	mvv_write(dev, 0x08, r8); /* capture rgb555/565, init DRAM, PC enable */
@@ -664,6 +668,7 @@ static int pms_capture(struct pms *dev, char __user *buf, int rgb555, int count)
 			len += dt;
 		}
 	}
+	kfree(tmp);
 	return len;
 }