ath9k: Check for pci_map_single() errors

pci_map_single() can fail so detect those errors with
pci_dma_mapping_error() and deal with them accordingly.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --cc drivers/net/wireless/ath9k/beacon.c
Simple merge

diff --cc drivers/net/wireless/ath9k/recv.c
Simple merge

diff --cc drivers/net/wireless/ath9k/xmit.c
Simple merge