shmem: fix double uncharge in __shmem_file_setup()

shmem: fix double uncharge in __shmem_file_setup()

If __shmem_file_setup() fails on struct file allocation it uncharges
memory commitment twice: first by shmem_unacct_size() and second time
implicitly in shmem_evict_inode() when it kills the newly created inode.

This patch removes shmem_unacct_size() from error path if the inode was
already there.

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>