brcmsmac: phy_lcn: remove duplicate code

Remove and refactor some code in order to avoid having identical code
for different branches.

Notice that this piece of code hasn't been modified since 2011.

Addresses-Coverity-ID: 1226756 ("Identical code for different branches")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>