fs/shmfs: Fix CONFIG_FS_SHM -> CONFIG_FS_SHMFS

The macro was wrong

fs/shm/CMakeLists.txt

@@ -20,6 +20,6 @@
 
 # Include POSIX message queue support
 
-if(CONFIG_FS_SHM)
+if(CONFIG_FS_SHMFS)
   target_sources(fs PRIVATE shm_open.c shm_unlink.c shmfs.c shmfs_alloc.c)
 endif()

fs/shm/Kconfig

@@ -19,4 +19,4 @@ config FS_SHMFS_VFS_PATH
 		The path to where shared memory objects will exist in the VFS
 		namespace.
 
-endif # FS_SHM
+endif # FS_SHMFS

fs/vfs/fs_stat.c

@@ -278,7 +278,7 @@ int inode_stat(FAR struct inode *inode, FAR struct stat *buf, int resolve)
     }
   else
 #endif
-#if defined(CONFIG_FS_SHM)
+#if defined(CONFIG_FS_SHMFS)
   /* Check for shared memory */
 
   if (INODE_IS_SHM(inode))