ext4: remove duplicated declarations in inode.c

ext4: remove duplicated declarations in inode.c

In patch b449ac27277a7652f41f4fa9a6ca7bf755d8651a, ext4_set_bh_endio
and ext4_end_io_buffer_write are declared at the beginning of inode.c,
and again later on in the middle of the file.  Remove the second set
of duplicated function declarations.

Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>