PCI: brcmstb: Fix broken brcm_pcie_mdio_write() polling

PCI: brcmstb: Fix broken brcm_pcie_mdio_write() polling

The MDIO_WT_DONE() macro tests bit 31, which is always 0 (== done) as
readw_poll_timeout_atomic() does a 16-bit read. Replace with the readl
variant.

[kwilczynski: commit log]
Fixes: ca5dcc76314d ("PCI: brcmstb: Replace status loops with read_poll_timeout_atomic()")
Link: https://lore.kernel.org/linux-pci/20240217133722.14391-1-wahrenst@gmx.net
Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Acked-by: Florian Fainelli <florian.fainelli@broadcom.com>