drivers/of: fix missing pr_cont()s in of_print_phandle_args

Since the KERN_CONT changes, the current debug printks have a lot of
empty lines making the log messages very hard to read.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Signed-off-by: Rob Herring <robh@kernel.org>