i2c: mxs: add missing kernel-doc for struct mxs_i2c_dev members

i2c: mxs: add missing kernel-doc for struct mxs_i2c_dev members

Add kernel-doc documentation for the struct members that were previously
undocumented. This fixes warnings when building with W=1 and ensures
the struct is fully documented per kernel-doc conventions.

Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20260603031135.289302-1-rosenp@gmail.com