net: wan/lmc: fix spelling of "its"

Use the possessive "its" instead of the contraction of "it is" ("it's")
in user messages.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>