[media] davinci: vpif: capture/display: fix race condition

channel_first_int[][] variable is used as a flag for the ISR,
This flag was being set after enabling the interrupts, There
where situations when the isr occurred even before the flag was set
dues to which it was causing the application hang.
This patch sets  channel_first_int[][] flag just before enabling the
interrupt.

Reported-by: David Oleszkiewicz <doleszki@adsyscontrols.com>
Signed-off-by: Lad, Prabhakar <prabhakar.lad@ti.com>
Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>