wl1251: fix always return 0 error

wl1251_event_ps_report() should not always return 0 because
wl1251_ps_set_mode() may fail. Change it to return 'ret'.

Fixes: f7ad1eed ("wl1251: retry power save entry")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200730073939.33704-1-wanghai38@huawei.com