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 <[e-mail]>
Signed-off-by: Jiapeng Chong <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Wei Liu <[e-mail]>

drivers/hv/hv_balloon.c

···
 		 * that need to be hot-added while ensuring the alignment
 		 * and size requirements of Linux as it relates to hot-add.
 		 */
-		region_start = pg_start;
 		region_size = (pfn_cnt / HA_CHUNK) * HA_CHUNK;
 		if (pfn_cnt % HA_CHUNK)
 			region_size += HA_CHUNK;