ata: sata_fsl: fix sscanf() and sysfs_emit() format strings

Use the %u format for unsigned int parameters handling with sscanf() and
sysfs_emit() to avoid compilation warnings. In
fsl_sata_rx_watermark_store(), the call to sscanf() to parse a single
argument is replaced with a call to kstrtouint().

While at it, also replace the printk(KERN_ERR) calls with dev_err()
calls and fix blank lines in fsl_sata_rx_watermark_store().

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>