'bgmac' is part of a managed resource allocated with bgmac_alloc(). It
should not be freed explicitly.
Remove the erroneous kfree() from the .remove() function.
Fixes: 34a5102c3235 ("net: bgmac: allocate struct bgmac just once & don't copy it"
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>