genesys: compute MAX_SCANNERS from array length

... of genesys_usb_device_list[]

backend/genesys.c

@@ -5978,7 +5978,7 @@ attach (SANE_String_Const devname, Genesys_Device ** devp, SANE_Bool may_wait)
   Genesys_Device *dev = 0;
   SANE_Int dn, vendor, product;
   SANE_Status status;
-  int i;
+  unsigned int i;
 
 
   DBG (DBG_proc, "attach: start: devp %s NULL, may_wait = %d\n",

backend/genesys_devices.c

@@ -3504,3 +3504,6 @@ static Genesys_USB_Device_Entry genesys_usb_device_list[] = {
   {0x04a9, 0x190a, &canon_lide_210_model},
   {0, 0, NULL}
 };
+
+#define MAX_SCANNERS (sizeof(genesys_usb_device_list) / \
+        sizeof(genesys_usb_device_list[0]))

backend/genesys_low.h

@@ -316,7 +316,6 @@ typedef enum Genesys_Color_Order
 Genesys_Color_Order;
 
 
-#define MAX_SCANNERS 50
 #define MAX_RESOLUTIONS 13
 #define MAX_DPI 4