arm: a37xx: pci: Don't spam about PIO Response Status

Use dev_dbg() instead of dev_err() in pcie_advk_check_pio_status().

For example CRS is not an error status, it just says that the request
should be retried.

Without this, U-Boot spams the terminal with
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x100000
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x108000
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x110000
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x120000
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x128000
  pcie_advk pcie@d0070000: Non-posted PIO Response Status: UR, 0xc80 @ 0x130000
  ...
when a device is not connected to a PCIe switch (Unsupported Request
from the switch).

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>