fbdev: msm: check for valid fence before using objects

Validate the input fence for mdss and sde rotator before
referencing the structure objects.
and also log the fence driver name waiting for the fence.
Earlier the fence name was null irrespective of the
driver.

Change-Id: Ie277d861057a41092505c73ef3815f7d769d114e
Signed-off-by: Raghavendra Ambadas <quic_c_rambad@quicinc.com>