staging: brcm80211: removed redundant code from brcms_c_set_gmode

The comment says the rateset is being cleared when switching to GMODE_LEGACY_B,
but the code that follows it does not do so. Besides, the rateset is already
valid at this point.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>