devtmpfs: convert to pr_fmt

Use the pr_fmt() macro to prefix all the output with "devtmpfs: ".
while at it, convert printk(<LEVEL>) to pr_<level>().

Signed-off-by: Longlong Xia <xialonglong1@huawei.com>
Link: https://lore.kernel.org/r/20230202033203.1239239-2-xialonglong1@huawei.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>