[SCSI] storvsc: Increase the value of STORVSC_MAX_IO_REQUESTS

Increase the value of STORVSC_MAX_IO_REQUESTS to 200 requests. The current
ringbuffer size can support this higher value.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>