Fix icom filter value, not ASCII!!!

https://github.com/Hamlib/Hamlib/issues/448

rigs/icom/icom.c

@@ -1868,7 +1868,7 @@ int icom_get_mode(RIG *rig, vfo_t vfo, rmode_t *mode, pbwidth_t *width)
 
     if (mode_len == 3)
     {
-        priv_data->filter = modebuf[2] - '0';
+        priv_data->filter = modebuf[2];
         rig_debug(RIG_DEBUG_TRACE,
                   "%s: modebuf[0]=0x%02x, modebuf[1]=0x%02x, modebuf[2]=0x%02x, mode_len=%d, filter=%d\n",
                   __func__, modebuf[0],

rigs/icom/icom.h

@@ -203,7 +203,7 @@ struct icom_priv_data
     int x25cmdfails;  // This will get set if the 0x25 command fails so we try just once
     int x1cx03cmdfails;  // This will get set if the 0x1c 0x03 command fails so we try just once
     int poweron;  // to prevent powering on more than once
-    int filter;   // Current filter selected 
+    unsigned char filter;   // Current filter selected 
 };
 
 extern const struct ts_sc_list r8500_ts_sc_list[];