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: f3cfd136aef0 ("of: restricted dma: Don't fail device probe on rmem init failure")
Cc: Will Deacon <[e-mail]>
Signed-off-by: David Brazdil <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

drivers/of/device.c

···
 			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");
 }