[PATCH v2] of: do not copy properties if they already exist in the destination

[Jonas Richardsen <jonasrichardsen@emlix.com>]

Currently `of_copy_property` copies the given property even if a property 
with the same name already exists on the destination node. 
This leads to kernel warnings about duplicate properties:
```
[    0.014063] Duplicate name in chosen, renamed to "stdout-path#1"
[    0.014093] Duplicate name in chosen, renamed to "bootargs#1"
[    0.014119] Duplicate name in chosen, renamed to "phandle#1"
[    0.014197] Duplicate name in reserved-memory, renamed to "#address-cells#1"
[    0.014226] Duplicate name in reserved-memory, renamed to "#size-cells#1"
[    0.014252] Duplicate name in reserved-memory, renamed to "ranges#1"
[    0.014278] Duplicate name in reserved-memory, renamed to "phandle#1"
```
Therefore, the function was changed to return an error if the property
already exists in the destination.
The change does not cause any regressions, because the only usage of
this function occurs within `arch/arm/boards/raspberry-pi/rpi-common.c`
where the original behaviour of the function is obviously unintended.

Signed-off-by: Jonas Richardsen <jonasrichardsen@emlix.com>
---
In the process of creating this patch, we realized that the fixups 
    for the Raspberry Pi are extensively copying properties from the video
    core device tree that are not strictly necessary. We will do some
    work on making the fixups more precise (i.e., only copy specific
    properties, not entire nodes) soon.

 drivers/of/base.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index b22959dabe..3192a74ab9 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -2346,6 +2346,9 @@ struct property *of_copy_property(const struct device_node *src,
 	if (!prop)
 		return NULL;
 
+	if (of_property_present(dst, propname))
+		return ERR_PTR(-EEXIST);
+
 	return of_new_property(dst, propname,
 			       of_property_get_value(prop), prop->length);
 }
-- 
2.42.0