msm: mdss: fb: check for empty timings list when initializing modes

While initializing modes, add additional check for empty timings list
and abort generating mode list if empty. Having empty list will lead
to setting an empty mode list, instead of keeping the default created
during framebuffer registration.

Change-Id: Ia03202d82d4e9a639a52e0e1b2ccbbdda3b6fcad
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>