video: fbdev: pxa3xx-gcu: Fix integer overflow in pxa3xx_gcu_write

[ Upstream commit a09d2d00af53b43c6f11e6ab3cb58443c2cac8a7 ]

In pxa3xx_gcu_write, a count parameter of type size_t is passed to words of
type int.  Then, copy_from_user() may cause a heap overflow because it is used
as the third argument of copy_from_user().

Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>