media: media/dvb: Use kmemdup rather than duplicating its implementation

[ Upstream commit f6af820ef1be58c2e4b81aa479b9f109eb6344ce ]

kmemdup is introduced to duplicate a region of memory in a neat way.
Rather than kmalloc/kzalloc + memcpy, which the programmer needs to
write the size twice (sometimes lead to mistakes), kmemdup improves
readability, leads to smaller code and also reduce the chances of mistakes.
Suggestion to use kmemdup rather than using kmalloc/kzalloc + memcpy.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Stable-dep-of: 8c64f4cdf4e6 ("media: edia: dvbdev: fix a use-after-free")
Signed-off-by: Sasha Levin <sashal@kernel.org>