UPSTREAM: zram: rename zram_decompress_page to __zram_bvec_read

UPSTREAM: zram: rename zram_decompress_page to __zram_bvec_read

zram_decompress_page naming is not proper because it doesn't decompress
if page was dedup hit or stored with compression.

Use more abstract term and consistent with write path function
__zram_bvec_write.

Link: http://lkml.kernel.org/r/1498459987-24562-4-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Juneho Choi <juno.choi@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 693dc1ce25b8c8fa33f930d47cd8f926eeb90812)
Signed-off-by: Peter Kalauskas <peskal@google.com>
Bug: 112488418
Change-Id: Ia7c948f4b78601458b7ebc23ab345d4bc0a8d4a8