pinctrl: rockchip: Fix smatch warning

pinctrl: rockchip: Fix smatch warning

This patch fix the following warning:
drivers/pinctrl/pinctrl-rockchip.c:1415 rockchip_set_drive_perpin() warn: inconsistent returns 'spin_lock:&bank->slock'.
  Locked on:   line 1377
               line 1384
               line 1393
  Unlocked on: line 1306
               line 1333
               line 1342
               line 1352
               line 1406
               line 1415
drivers/pinctrl/pinctrl-rockchip.c:1415 rockchip_set_drive_perpin() warn: inconsistent returns 'irqsave:flags'.
  Locked on:   line 1377
               line 1384
               line 1393
  Unlocked on: line 1306
               line 1333
               line 1342
               line 1352
               line 1406
               line 1415

Change-Id: I3f97010fbc283084f06b83afcc46ab684d2a11c3
Signed-off-by: David Wu <david.wu@rock-chips.com>