media: af9035: prevent buffer overflow on write

When less than 3 bytes are written to the device, memcpy is called with
negative array size which leads to buffer overflow and kernel panic. This
patch adds a condition and returns -EOPNOTSUPP instead.
Fixes bugzilla issue 64871

[mchehab+samsung@kernel.org: fix a merge conflict and changed the
 condition to match the patch's comment, e. g. len == 3 could
 also be valid]
Signed-off-by: Jozef Balga <jozef.balga@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>