staging: rtl8723bs: Improve clarity of MAR usage

staging: rtl8723bs: Improve clarity of MAR usage

This patch improves the readability of the code related to the Multicast
Address Register (REG_MAR) in the rtl8723bs driver. It adds comments to
clarify the purpose and offset of the register, making the code more
self-documenting without introducing new macros.

Signed-off-by: Manjae Cho <manjae.cho@samsung.com>
Reviewed-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>
Link: https://lore.kernel.org/r/20240731225134.917542-1-manjae.cho@samsung.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>