tmpfs: push VEXEC check into tmpfs_lookup()
vfs_cache_lookup() has already done the appropriate VEXEC check, therefore
we must not re-check in VOP_CACHEDLOOKUP.
This fixes O_SEARCH semantics on tmpfs and removes a redundant descent into
VOP_ACCESS() in the common case.
Reported-by: arichardson (via CheriBSD Jenkins CI)
MFC-after: 3 days
Differential Revision: https://reviews.freebsd.org/D28401