fpga: prevent integer overflow in dfl_feature_ioctl_set_irq()

fpga: prevent integer overflow in dfl_feature_ioctl_set_irq()

[ Upstream commit 939bc5453b8cbdde9f1e5110ce8309aedb1b501a ]

The "hdr.count * sizeof(s32)" multiplication can overflow on 32 bit
systems leading to memory corruption.  Use array_size() to fix that.

Fixes: 322b598be4d9 ("fpga: dfl: introduce interrupt trigger setting API")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/YxBAtYCM38dM7yzI@kili
Signed-off-by: Xu Yilun <yilun.xu@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>