Adopted implied LFS_O_FLUSH bit pattern in LFS_O_SYNC

LFS_O_SYNC always implies LFS_O_FLUSH, otherwise what exactly are you
syncing? Making this explicit in the bit pattern should hopefully make
this clear for curious users, though lfsr_file_flush would be called
anyways because of how lfsr_file_sync is implemented.

This also moves the LFS_O_DESYNC bit pattern around so SYNC/FLUSH are
neighbors. SYNC/DESYNC may seem related, but in lfsr_file_open they
actually are quite different:

  LFS_O_FLUSH   0x0040  ---- ---- -1-- ----
  LFS_O_SYNC    0x00c0  ---- ---- 11-- ----
  LFS_O_DESYNC  0x0100  ---- ---1 ---- ----

Code changes, mostly just noise from moving bits around:

           code          stack
  before: 35228           2680
  after:  35244 (+0.0%)   2680 (+0.0%)

lfs.c

@@ -9760,18 +9760,18 @@ static inline bool lfsr_o_isappend(uint32_t flags) {
     return flags & LFS_O_APPEND;
 }
 
+static inline bool lfsr_o_isflush(uint32_t flags) {
+    return flags & LFS_O_FLUSH;
+}
+
 static inline bool lfsr_o_issync(uint32_t flags) {
-    return flags & LFS_O_SYNC;
+    return flags & (LFS_O_SYNC ^ LFS_O_FLUSH);
 }
 
 static inline bool lfsr_o_isdesync(uint32_t flags) {
     return flags & LFS_O_DESYNC;
 }
 
-static inline bool lfsr_o_isflush(uint32_t flags) {
-    return flags & LFS_O_FLUSH;
-}
-
 static inline bool lfsr_f_isunflush(uint32_t flags) {
     return flags & LFS_F_UNFLUSH;
 }

lfs.h

@@ -137,9 +137,9 @@ enum lfs_open_flags {
     LFS_O_EXCL      = 0x0008,   // Fail if a file already exists
     LFS_O_TRUNC     = 0x0010,   // Truncate the existing file to zero size
     LFS_O_APPEND    = 0x0020,   // Move to end of file on every write
-    LFS_O_SYNC      = 0x0040,   // Sync metadata on every write
-    LFS_O_DESYNC    = 0x0080,   // Do not sync or recieve file updates
-    LFS_O_FLUSH     = 0x0100,   // Flush data on every write
+    LFS_O_FLUSH     = 0x0040,   // Flush data on every write
+    LFS_O_SYNC      = 0x00c0,   // Sync metadata on every write
+    LFS_O_DESYNC    = 0x0100,   // Do not sync or recieve file updates
 #endif
 
     // internally used flags