ata: ahci_platform: fix ahci_platform_data->suspend method handling

Looking at ST SPEAr1340 AHCI code (the only user of the deprecated
pdata->suspend and pdata->resume) it is obvious the we should return
after calling pdata->suspend() only if the function have returned
non-zero return value.  The code has been broken since commit 1e70c2
("ata/ahci_platform: Add clock framework support").  Fix it.

Cc: Viresh Kumar <viresh.linux@gmail.com>
Cc: Shiraz Hashim <shiraz.hashim@st.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>