wlan: fix compilation errors for PNO and ROAM_SCAN_OFFLOAD feature flags

WLAN driver fails to compile once FEATURE_WLAN_SCAN_PNO and
FEATURE_ROAM_SCAN_OFFLOAD are disabled in KBUILD.

Patch takescare of reported build failures when either or both of
features are disabled.

Change-Id: Iaaf9653653ca5e0c1805c2a97709b68f8b90a699
CRs-Fixed: 572897
diff --git a/CORE/SME/src/csr/csrApiScan.c b/CORE/SME/src/csr/csrApiScan.c
index 193cec7..6d8b0d3 100644
--- a/CORE/SME/src/csr/csrApiScan.c
+++ b/CORE/SME/src/csr/csrApiScan.c
@@ -7908,6 +7908,7 @@
     return fValid;
 }
 
+#ifdef FEATURE_WLAN_SCAN_PNO
 eHalStatus csrScanSavePreferredNetworkFound(tpAniSirGlobal pMac,
             tSirPrefNetworkFoundInd *pPrefNetworkFoundInd)
 {
@@ -8077,6 +8078,7 @@
 
    return eHAL_STATUS_SUCCESS;
 }
+#endif //FEATURE_WLAN_SCAN_PNO
 
 #ifdef FEATURE_WLAN_LFR
 void csrInitOccupiedChannelsList(tpAniSirGlobal pMac)