fix compile warning

[DeeNewcum]

This fixes the following compile warning:

pi400kb/pi400.c: In function ‘modprobe_libcomposite’:                                                                                                                                         
pi400kb/pi400.c:82:37: warning: passing argument 2 of ‘execv’ from incompatible pointer type [-Wincompatible-pointer-types]                                                                   
   82 |         execv("/usr/sbin/modprobe", argv);                                                                                                                                            
      |                                     ^~~~                                                                                                                                              
      |                                     |                                                                                                                                                 
      |                                     const char **                                                                                                                                     
In file included from pi400kb/pi400.c:14:                                                                                                                                                     
/usr/include/unistd.h:563:51: note: expected ‘char * const*’ but argument is of type ‘const char **’                                                                                          
  563 | extern int execv (const char *__path, char *const __argv[])                                                                                                                           
      |                                       ~~~~~~~~~~~~^~~~~~~~                                                                                                                            

[Gadgetoid]

Aha! Thank you!