video: msm: Do not use disable_irq in the spin_lock_irqsave context

Both mdp_isr() and mdp_histogram_disable() uses the same
spin lock mdp_spin_lock variable.  One core waits for disabling
mdp_isr after acquiring mdp_spin_lock and other core in mdp_isr()
waits for spin lock mdp_spin_lock and dead lock between two cores.

Change-Id: I73a10494ab78e92fc88a348aed4f526091b51f89
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>