staging: brcm80211: remove MIPS specific 'sync' instruction in fullmac

This instruction was required for the bcm4716/bcm4322, but since the
fullmac driver only supports bcm4329, it could be removed. After that,
the R_REG macro's were identical and thus were reduced to just 1 R_REG
macro.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>