Added some noise immunity to vsync

Change-Id: I7a678fdab841f009742ed2f9857f7d1b83515b45

src/rgb_to_fb.S

@@ -35,12 +35,20 @@ wait_for_vsync_a:
         ldr    r8, [r4]
         tst    r8, #VSYNC_MASK
         beq    wait_for_vsync_a
+        // Check again in case of noise
+        ldr    r8, [r4]
+        tst    r8, #VSYNC_MASK
+        beq    wait_for_vsync_a
 
         // Wait for end of vsync
 wait_for_vsync_b:
         ldr    r8, [r4]
         tst    r8, #VSYNC_MASK
         bne    wait_for_vsync_b
+        // Check again in case of noise
+        ldr    r8, [r4]
+        tst    r8, #VSYNC_MASK
+        bne    wait_for_vsync_b
 
         // Skip inactive lines
         mov    r5, #28