hv_balloon: Remove redundant assignment to region_start

hv_balloon: Remove redundant assignment to region_start

Variable region_start is set to pg_start but this value is never
read as it is overwritten later on, hence it is a redundant
assignment and can be removed.

Cleans up the following clang-analyzer warning:

drivers/hv/hv_balloon.c:1013:3: warning: Value stored to 'region_start'
is never read [clang-analyzer-deadcode.DeadStores].

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1619691681-86256-1-git-send-email-jiapeng.chong@linux.alibaba.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>