xbc_calc_checksum() only reads the data buffer, so mark the parameter
as const void * and the internal pointer as const unsigned char *.
Link: https://lore.kernel.org/all/20260318155919.78168-7-objecting@objecting.org/
Signed-off-by: Josh Law <objecting@objecting.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
306c36a76d