apps: common: image: Fix assertion

`plane` must be strictly less than the vector's size,
it cannot be equal to it.

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/apps/common/image.cpp

@@ -98,12 +98,12 @@ unsigned int Image::numPlanes() const
 
 Span<uint8_t> Image::data(unsigned int plane)
 {
-	assert(plane <= planes_.size());
+	assert(plane < planes_.size());
 	return planes_[plane];
 }
 
 Span<const uint8_t> Image::data(unsigned int plane) const
 {
-	assert(plane <= planes_.size());
+	assert(plane < planes_.size());
 	return planes_[plane];
 }