Fix broken texinfo

@ must be escaped as @@

Author: dl8dtl

src/doc/avrdude.texi

@@ -1561,7 +1561,7 @@ Info: Writing 24 bytes starting from address 0x00
 avrdude> dump eeprom 0 32
 >>> dump eeprom 0 32 
 
-0000  d2 02 96 49 41 56 52 55  f8 2d 40 48 65 6c 6c 6f  |...IAVRU.-@Hello|
+0000  d2 02 96 49 41 56 52 55  f8 2d 40 48 65 6c 6c 6f  |...IAVRU.-@@Hello|
 0010  20 57 6f 72 6c 64 21 00  ff ff ff ff ff ff ff ff  | World!.........|
 
 avrdude> q