[PATCH] reiserfs: add missing D-cache flushing

Looks like, reiserfs_prepare_file_region_for_write() doesn't contain
several flush_dcache_page() calls.

Found with help from Dmitriy Monakhov <dmonakhov@openvz.org>

[akpm@osdl.org: small speedup]
Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Cc: Dmitriy Monakhov <dmonakhov@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>