Wunused-variable: Fixed all unused variables in src

This commit addresses all warnings emitted from -Wunused-variable
in the C++ src.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/zfm20/zfm20.cxx

@@ -90,7 +90,6 @@ bool ZFM20::dataAvailable(unsigned int millis)
   timeout.tv_sec = 0;
   timeout.tv_usec = millis * 1000;
 
-  int nfds;  
   fd_set readfds;
 
   FD_ZERO(&readfds);
@@ -281,7 +280,6 @@ bool ZFM20::getResponse(uint8_t *pkt, int len)
   int idx = 0;
   int timer = 0;
   int rv;
-  int plen = 0;
 
   while (idx < len)
     {