shmem_read_mapping_page_gfp always returns an uptodate page or an
ERR_PTR.  Remove the code that tries to handle a non-uptodate page.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>