staging: atomisp: remove "fun" strncpy warning

[for older kernels only, atomisp has been removed from upstream]

gcc-8 rightfully warns that this instance of strncpy is just copying
from the source, to the same source, for a few bytes.  Meaning this call
does nothing.  As the author of the code obviously meant it to do
something, but this code must be working properly, just replace the call
to the kernel internal strscpy() which gcc doesn't know about, so the
warning goes away.

As this driver was deleted from newer kernel versions, none of this
really matters but now at least we do not have to worry about a build
warning in the stable trees.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>