main_help.c: Do not care what char is returned by getchar()

CID 1437650: Unchecked return value from library in rtems_shell_help().

Closes #4291

cpukit/libmisc/shell/main_help.c

@@ -148,7 +148,7 @@ static int rtems_shell_help(
         line+= rtems_shell_help_cmd(shell_cmd);
       if (lines && (line > lines)) {
         printf("Press any key to continue...");
-        getchar();
+        (void) getchar();
         printf("\n");
         line = 0;
       }