Update usb_host_client_config_t struct

[cojopi]

In Arduino-ESP32, IDF release/v4.4 #5911 the structure of usb_host_client_config_t changed. This change fix the client_config to be able to compile with ESP-IDF v4.4 on latest Arduino-ESP32 release.

[lyusupov]

.callback_arg = NULL

• causes a system panic

Guru Meditation Error: Core  0 panic'ed (LoadProhibited). Exception was unhandled.                                                            
                                                                                                                                              
Core  0 register dump:                                                                                                                        
PC      : 0x400d204d  PS      : 0x00060d30  A0      : 0x80102396  A1      : 0x3ffdf9b0                                                        
A2      : 0x3ffdf9d8  A3      : 0x00000000  A4      : 0x3ffdf1f4  A5      : 0x00000000                                                        
A6      : 0x00000000  A7      : 0x40101c94  A8      : 0x00000000  A9      : 0x3ffdf970                                                        
A10     : 0x3ffdf9d8  A11     : 0x3ffdf9d8  A12     : 0x00060d20  A13     : 0x3ffc66e4                                                        
A14     : 0x00000001  A15     : 0x00000001  SAR     : 0x0000000c  EXCCAUSE: 0x0000001c                                                        
EXCVADDR: 0x00000010  LBEG    : 0x00060d20  LEND    : 0x3ffc66e4  LCOUNT  : 0x40028c39                                                        
                                                                                                                                                                                                                                                                                        
Backtrace:0x400d204a:0x3ffdf9b00x40102393:0x3ffdf9d0 0x400d1f7e:0x3ffdfa00 

while reverting back this part of the PR:

.callback_arg = this

• then it fixes the issue.