[MIPS] pnx8550: Fix write_config_byte() PCI config space accessor

[MIPS] pnx8550: Fix write_config_byte() PCI config space accessor

There's a serious typo in the function:
  arch/mips/pci/ops-pnx8550.c:write_config_byte()

The parameter passed to the function config_access() is PCI_CMD_CONFIG_READ
instead of PCI_CMD_CONFIG_WRITE. This renders any attempts to write
a single byte to the PCI configuration registers useless.

This problem does not exist for write_config_word() nor write_config_dword().

This problem has been there since kernel v2.6.17 and is still there
as of kernel v2.6.19.1.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>