ssb: Use true and false for bool variable

Fix the following coccicheck warnings:

./include/linux/ssb/ssb_driver_gige.h:89:8-9: WARNING: return of 0/1 in
function 'ssb_gige_one_dma_at_once' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:79:8-9: WARNING: return of 0/1 in
function 'ssb_gige_have_roboswitch' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:182:8-9: WARNING: return of 0/1 in
function 'ssb_gige_must_flush_posted_writes' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:178:8-9: WARNING: return of 0/1 in
function 'ssb_gige_one_dma_at_once' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:174:8-9: WARNING: return of 0/1 in
function 'ssb_gige_have_roboswitch' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:170:8-9: WARNING: return of 0/1 in
function 'ssb_gige_is_rgmii' with return type bool.

./include/linux/ssb/ssb_driver_gige.h:162:8-9: WARNING: return of 0/1 in
function 'pdev_is_ssb_gige_core' with return type bool.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Acked-by: Michael Büsch <m@bues.ch>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1612508199-92282-1-git-send-email-jiapeng.chong@linux.alibaba.com