staging: sm750fb: Fix the power state error in resume

The PM_EVENT_RESUME state is needed when SM750 resume, otherwise it
will be failed in the second time of continuous suspend/resume.

Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Binbin Zhou <zhoubb@lemote.com>
Reviewed-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Teddy Wang <teddy.wang@siliconmotion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>