vulkan: fix compile error with latest AHB changes

Otherwise, the following error is observed:

frameworks/native/vulkan/include/vulkan/vk_android_native_buffer.h:128:5:
   error: must use 'struct' tag to refer to type 'AHardwareBuffer'

BUG=313466265
TEST=presubmit

Change-Id: I1d32208a26161a64cba057a9fb4a47ce28b83d5b