make dtbs_check:

    $nodename:0: 'i2c-10' does not match '^(i2c-?)?mux'

Fix this by renaming all I2C bus demultiplexer node names to
"i2c-mux<N>".
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/63e97cb50282b3255ba9654f539b9baa8c621b30.1698068647.git.geert+renesas@glider.be