NFS: FMODE_READ and friends are C macros, not enum types

Address a sparse warning:

  CHECK   fs/nfs/nfstrace.c
fs/nfs/nfstrace.c: note: in included file (through /home/cel/src/linux/rpc-over-tls/include/trace/trace_events.h, /home/cel/src/linux/rpc-over-tls/include/trace/define_trace.h, ...):
fs/nfs/./nfstrace.h:424:1: warning: incorrect type in initializer (different base types)
fs/nfs/./nfstrace.h:424:1:    expected unsigned long eval_value
fs/nfs/./nfstrace.h:424:1:    got restricted fmode_t [usertype]
fs/nfs/./nfstrace.h:425:1: warning: incorrect type in initializer (different base types)
fs/nfs/./nfstrace.h:425:1:    expected unsigned long eval_value
fs/nfs/./nfstrace.h:425:1:    got restricted fmode_t [usertype]
fs/nfs/./nfstrace.h:426:1: warning: incorrect type in initializer (different base types)
fs/nfs/./nfstrace.h:426:1:    expected unsigned long eval_value
fs/nfs/./nfstrace.h:426:1:    got restricted fmode_t [usertype]

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>