mac80211: rt2x00: fix PCI eeprom patch

Fixes the following warnings:

  CC [M] <...>/drivers/net/wireless/rt2x00/rt2800pci.o
<...>/drivers/net/wireless/rt2x00/rt2800pci.c: In function 'rt2800pci_read_eeprom_file':
<...>/drivers/net/wireless/rt2x00/rt2800pci.c:95:2: warning: 'return' with a value, in function returning void [enabled by default]
<...>/drivers/net/wireless/rt2x00/rt2800pci.c: In function 'rt2800pci_read_eeprom':
<...>/drivers/net/wireless/rt2x00/rt2800pci.c:994:2: warning: 'retval' may be used uninitialized in this function [-Wuninitialized]

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35143 3c298f89-4303-0410-b956-a3cf2f4a3e73