qca_spi: Add QCASPI prefix to ring defines

All defines in qca_spi.h except of the two ring limit defines have
a QCASPI prefix. Since the name is quite generic add the QCASPI prefix
to avoid possible name conflicts.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>