i2c: octeon: fix return commenting

i2c: octeon: fix return commenting

Kernel-docs require a ':' to signify the return behaviour of a function
with within the comment. Many functions in this file were missing ':'
after the "Returns" line, resulting in kernel-doc warnings.

Add the ':' to satisfy kernel-doc requirements.

Signed-off-by: Aryan Srivastava <aryan.srivastava@alliedtelesis.co.nz>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/20250318021632.2710792-2-aryan.srivastava@alliedtelesis.co.nz
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>