mm/shmem: remove unneeded assignments in shmem_get_folio_gfp()

mm/shmem: remove unneeded assignments in shmem_get_folio_gfp()

After the rework of shmem_get_folio_gfp() to use a folio, the local
variable hindex is only needed to be set once before passing it to
shmem_add_to_page_cache().

Remove the unneeded initialization and assignments of the variable hindex
before the actual effective assignment and first use.

No functional change. No change in object code.

Link: https://lkml.kernel.org/r/20221007085027.6309-1-lukas.bulwahn@gmail.com
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>