net: dsa: sja1105: Remove unneeded cast in sja1105_crc32()

sja1105_unpack() takes a "const void *buf" as its first parameter, so
there is no need to cast away the "const" of the "buf" variable before
calling it.

Drop the cast, as it prevents the compiler performing some checks.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20210223112003.2223332-1-geert+renesas@glider.be


Signed-off-by: Jakub Kicinski <kuba@kernel.org>