of: Remove superfluous casts when printing u64 values

"u64" is "unsigned long long" on all architectures now.  Hence there is
no longer a need to use casts when formatting using the "ll" length
modifier.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/ef3f4f78385b43230695ba0855d078290c958192.1623835273.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>