of: restricted dma: Fix condition for rmem init

of_dma_set_restricted_buffer fails to handle negative return values from
of_property_count_elems_of_size, e.g. when the property does not exist.
This results in an attempt to assign a non-existent reserved memory
region to the device and a warning being printed. Fix the condition to
take negative values into account.

Fixes: f3cfd13 ("of: restricted dma: Don't fail device probe on rmem init failure")
Cc: Will Deacon <will@kernel.org>
Signed-off-by: David Brazdil <dbrazdil@google.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210917131423.2760155-1-dbrazdil@google.com
Signed-off-by: Rob Herring <robh@kernel.org>

Author: David Brazdil

drivers/of/device.c

@@ -85,7 +85,11 @@ of_dma_set_restricted_buffer(struct device *dev, struct device_node *np)
 			break;
 	}
 
-	if (i != count && of_reserved_mem_device_init_by_idx(dev, of_node, i))
+	/*
+	 * Attempt to initialize a restricted-dma-pool region if one was found.
+	 * Note that count can hold a negative error code.
+	 */
+	if (i < count && of_reserved_mem_device_init_by_idx(dev, of_node, i))
 		dev_warn(dev, "failed to initialise \"restricted-dma-pool\" memory node\n");
 }