Replaced SERIAL_PROTOCOLPGM(MSG_BED) with SERIAL_PROTOCOLPGM("Bed")

Resolved some warnings in Marlin_main.cpp regarding compares of signed and unsigned integers by replacing 'int' or 'uint16_t' with 'uint8_t'.

Marlin/Marlin_main.cpp

       feedrate = homing_feedrate[Z_AXIS];
 
       run_z_probe();
-      SERIAL_PROTOCOLPGM(MSG_BED);
+      SERIAL_PROTOCOLPGM("Bed");
       SERIAL_PROTOCOLPGM(" X: ");
       SERIAL_PROTOCOL(current_position[X_AXIS] + 0.0001);
       SERIAL_PROTOCOLPGM(" Y: ");
   inline void gcode_M48() {
 
     double sum = 0.0, mean = 0.0, sigma = 0.0, sample_set[50];
-    int verbose_level = 1, n_samples = 10, n_legs = 0;
-    
+    uint8_t verbose_level = 1, n_samples = 10, n_legs = 0;
+
     if (code_seen('V') || code_seen('v')) {
       verbose_level = code_value_short();
       if (verbose_level < 0 || verbose_level > 4 ) {
 
     if (deploy_probe_for_each_reading) stow_z_probe();
 
-    for (uint16_t n=0; n < n_samples; n++) {
+    for (uint8_t n=0; n < n_samples; n++) {
 
       do_blocking_move_to(X_probe_location, Y_probe_location, Z_start_location); // Make sure we are at the probe location
 
         //SERIAL_ECHOPAIR("   direction: ",dir);
         //SERIAL_EOL;
 
-        for (int l = 0; l < n_legs - 1; l++) {
+        for (uint8_t l = 0; l < n_legs - 1; l++) {
           ms = millis();
           theta += RADIANS(dir * (ms % 20L));
           radius += (ms % 10L) - 5L;
       // Get the current mean for the data points we have so far
       //
       sum = 0.0;
-      for (int j = 0; j <= n; j++) sum += sample_set[j];
+      for (uint8_t j = 0; j <= n; j++) sum += sample_set[j];
       mean = sum / (n + 1);
 
       //
       // data points we have so far
       //
       sum = 0.0;
-      for (int j = 0; j <= n; j++) {
+      for (uint8_t j = 0; j <= n; j++) {
         float ss = sample_set[j] - mean;
         sum += ss * ss;
       }