staging: brcm80211: simplified register access macro's in softmac

Code cleanup. Removed MIPS specific 'sync' instruction since this is not
required for the chips that this driver supports. MIPS specific macro's
were now the same as non-MIPS register access macro's and thus have been
deleted. Also added comment that makes clearer what the benefit of these
macro's is. Unified big and little end register access macro's.

Reported-by: Dan Carpenter <error27@gmail.com>
Reported-by: Julian Calaby <julian.calaby@gmail.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>