clk: si5351: Update datasheet references

Silicon Labs is now part of Skyworks Inc. so update the URLs to the
datasheet and application note.

Signed-off-by: Jens Renner <renner@efe-gmbh.de>
Link: https://lore.kernel.org/r/20210913074823.115212-1-renner@efe-gmbh.de


Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>