gbl: Fix incorrect GblEfiBootMemoryProtocol GUID in libefi_types

This change updates GblEfiBootMemoryProtocol::GUID in libefi_types
from the EFI Block I/O Protocol GUID to canonical
GBL_EFI_BOOT_MEMORY_PROTOCOL_GUID (309F2874-AD59-4FD2-AF5E-CE0F4AB401A6),
matching libefi and documentation.

Test: ./bazel.sh test @gbl//tests
Change-Id: Iae9f12b5406fcea04624ff352f9fe6113aaa2aca

bootable/libbootloader

diff --git a/bootable/libbootloader b/bootable/libbootloader
index 451724e..b43f536 160000
--- a/bootable/libbootloader
+++ b/bootable/libbootloader
@@ -1 +1 @@
-Subproject commit 451724e63e0cdce6b0199001d16c0c6950f19baa
+Subproject commit b43f536aeea02d0841d4dbf14b96e415f2b14ec2