staging: prima: Fix -Warray-bounds

Silence this warning by changes PHY_MAX_RX_CHAINS into 1 which is defined in typedef enum

../drivers/staging/prima/CORE/HDD/src/wlan_hdd_ftm.c:4741:19: warning: array index 1 is past the end of the array (which contains 1 element)
      [-Warray-bounds]
                  pMsgBody->GetRxRssi.rssi.rx[1]);
                  ^                           ~
../drivers/staging/prima/riva/inc/wlan_phy.h:299:5: note: array 'rx' declared here
    tANI_U8 rx[PHY_MAX_RX_CHAINS];
    ^

Change-Id: Ie36e8ae8e9c5beb484840b9f9aa5193dee13df69
Signed-off-by: khusika <khusikadhamar@gmail.com>