apm821xx: fix atheros PCIe cards on the MR24

The consolidation of the MR24 and WNDR4700 subtargets
into the nand subtarget broke MR24's atheros wlan.
This was because the wndr4700's board code used a
pci_fixup routines to supply the ath9k module with
the calibration data.

This is not necessary on the MR24 as it has standard
mini-pcie ports. Hence the two AR9380 mini-pcie cards
do not need any calibration data overrides.

Cc: chrisrblake93@gmail.com
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>