mdss: display: add spin_lock to mdss_disable_irq_nosync()

Add spin_lock to mdss_lock inside mdss_disable_irq_nosync
to avoid race condition which can cause mdss_irq to be disabled
while irq_mask bits are still set.

CRs-Fixed: 624806
Change-Id: I44074a057dff49dfc7a4d2829f3c4e599dca4a69
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>