vrend: fix missed flagging as GBM_BUFFER on early-return
A recent refactor incorrectly moved GBM_BUFFER flagging after a non-error early-return in vrend_resource_gbm_init.
This regresses Android CTS, causing failed buffer mapping.
Fixes: 511f4506 ("Fix vrend_resource_gbm_init() error handling")
Signed-off-by: Ryan Neph ryanneph@google.com