staging: mt7621-mmc: replace `printk` with preferred API

Replace calls to `printk` with `dev_info` and `pr_err`
Issues found with checkpatch.pl

Signed-off-by: Dafna Hirschfeld <dafna3@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>