scsi: esas2r: Use FIELD_GET() to extract PCIe capability fields

scsi: esas2r: Use FIELD_GET() to extract PCIe capability fields

Use FIELD_GET() to extract PCIe capability register fields instead of
custom masking and shifting. Also remove the unnecessary cast to u8, the
value in those fields always fits to u8.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230913122748.29530-8-ilpo.jarvinen@linux.intel.com
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>