fs: Let files_allocate return -EMFILE instead ERROR

since the internal function normally return the error code directly

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Ifccbcfb07d2f8f7d5fef1b2a867538f51b73655c

fs/inode/fs_files.c

@@ -336,7 +336,7 @@ int files_allocate(FAR struct inode *inode, int oflags, off_t pos, int minfd)
     }
 
   _files_semgive(list);
-  return ERROR;
+  return -EMFILE;
 }
 
 /****************************************************************************

fs/vfs/fs_dupfd.c

@@ -60,7 +60,7 @@ int file_dup(FAR struct file *filep, int minfd)
   fd2 = files_allocate(NULL, 0, 0, minfd);
   if (fd2 < 0)
     {
-      return -EMFILE;
+      return fd2;
     }
 
   ret = fs_getfilep(fd2, &filep2);

fs/vfs/fs_open.c

@@ -207,7 +207,7 @@ int nx_vopen(FAR const char *path, int oflags, va_list ap)
   fd = files_allocate(inode, oflags, 0, 0);
   if (fd < 0)
     {
-      ret = -EMFILE;
+      ret = fd;
       goto errout_with_inode;
     }