net: usb: Add SMSC copyright to smsc95xx driver

This driver was upstreamed without an SMSC copyright, even thought it seems
that SMSC was the original author.

See the kernel version for a code comparison:

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=2f7ca802bdae2ca41022618391c70c2876d92190



It's not clear who actually moved this code, or whether the kernel was the
original source, or somewhere else, but it probably should still have the
SMSC copyright.

Signed-off-by: Simon Glass <sjg@chromium.org>