drivers/char: make serial_parse_handle take const argument

It doesn't modify it, and it will be necessary in a subsequent patch.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/char/serial.c

@@ -301,7 +301,7 @@ char serial_getc(int handle)
     return c & 0x7f;
 }
 
-int __init serial_parse_handle(char *conf)
+int __init serial_parse_handle(const char *conf)
 {
     int handle, flags = 0;
 

xen/include/xen/serial.h

@@ -109,7 +109,7 @@ void serial_init_postirq(void);
 void serial_endboot(void);
 
 /* Takes a config string and creates a numeric handle on the COM port. */
-int serial_parse_handle(char *conf);
+int serial_parse_handle(const char *conf);
 
 /* Transmit a single character via the specified COM port. */
 void serial_putc(int handle, char c);