cmd: fdt: Fix fdt rm behavior on non-existent property and error message space

cmd: fdt: Fix fdt rm behavior on non-existent property and error message space

In case an FDT contains a node '/test-node@1234' , with no property
called 'noprop' in that node, the following command triggers a print
of help message for 'fdt' command instead of erroring out:
=> fdt rm /test-node@1234 noprop
This is because the subcommand errornously returns 'err' instead of
CMD_RET_FAILURE, fix it. Furthermore, align the number of spaces past
fdt_delprop() in error message with the rest of the code.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Simon Glass <sjg@chromium.org>