cpu: stm32f2: periph: timer: fix interrupt handler.
cpu: stm32f2: periph: timer: fix interrupt handler.

Signed-off-by: Takeyoshi Kikuchi <af72ecfe6d0bf60ad0be9363518c74b6bed5ff74@centurysys.co.jp>
(cherry picked from commit 30eb6f50368526ee9463a2ca31693876b4463f7c)
Signed-off-by: Takeyoshi Kikuchi <af72ecfe6d0bf60ad0be9363518c74b6bed5ff74@centurysys.co.jp>
(cherry picked from commit 884d20f5cf912833131f272a8f53acbff1f76bbf)

centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT,centurysys/RIOT