Increases fastbootd response message size

Some output of `fastboot getvar` exceeds current message size.
Increases the message size to 256 to fix the issue.

Bug: 74445765
Bug: 144473561
Test: fastboot getvar system-fingerprint
Change-Id: Id5064be4bb500697ce87c473f662d86c7c344d65
diff --git a/fastboot/constants.h b/fastboot/constants.h
index aefd448..ba43ca5 100644
--- a/fastboot/constants.h
+++ b/fastboot/constants.h
@@ -42,7 +42,7 @@
 #define RESPONSE_INFO "INFO"
 
 #define FB_COMMAND_SZ 64
-#define FB_RESPONSE_SZ 64
+#define FB_RESPONSE_SZ 256
 
 #define FB_VAR_VERSION "version"
 #define FB_VAR_VERSION_BOOTLOADER "version-bootloader"