msm_fb: Fail fb2 open during suspend if ref_cnt is zero

Fail fb2 open during suspend if the ref_cnt for fb2 is zero
currently.

CRs-fixed: 475310
Change-Id: Ie5dd7c2dadecb489423cca1e2ff8276edc6314d7
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>