libfdt: Fix fdt_appendprop_addrrange documentation

According to the documentation, the function should default to the very
common property name <reg> when none is "specified". However, neither
passing NULL (ends up calling strlen(NULL) and segfaults) nor ""
(appends a property with an empty name) implements this behavior.

Furthermore, the test case supposed to cover this default value actually
passes the value to the function, somewhat defeating its own purpose:

    /* 2. default property name */

    // ...

    err = fdt_appendprop_addrrange(fdt, 0, offset, "reg", addr, size);
    if (err)
            FAIL("Failed to set \"reg\": %s", fdt_strerror(err));
    check_getprop_addrrange(fdt, 0, offset, "reg", 1);

Finally, nothing in the implementation of the function seems to attempt
to cover that use-case.

As the feature can't ever have been used by clients and as the resulting
reduced readability of the caller seems (IMO) to outweigh any potential
benefit this API would bring, remove the erroneous documentation instead
of trying to fix the function.

Reported-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
Message-ID: <20230831123918.rf54emwkzgtcb7aw@google.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/libfdt.h

@@ -2029,7 +2029,7 @@ static inline int fdt_appendprop_cell(void *fdt, int nodeoffset,
  * address and size) to the value of the named property in the given
  * node, or creates a new property with that value if it does not
  * already exist.
- * If "name" is not specified, a default "reg" is used.
+ *
  * Cell sizes are determined by parent's #address-cells and #size-cells.
  *
  * This function may insert data into the blob, and will therefore