xz: fix XZ_DYNALLOC to avoid useless memory reallocations

xz: fix XZ_DYNALLOC to avoid useless memory reallocations

s->dict.allocated was initialized to 0 but never set after a successful
allocation, thus the code always thought that the dictionary buffer has
to be reallocated.

Link: http://lkml.kernel.org/r/20191104185107.3b6330df@tukaani.org
Reported-by: Yu Sun <yusun2@cisco.com>
Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Acked-by: Daniel Walker <danielwa@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 8e20ba2e53fc
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>