ipmi: remove open coded version of SMBus block write

The block-write function of the core was not used because there was no
client-struct to use. However, in this case it seems apropriate to use a
temporary client struct. Because we are answering a request we recieved
when being a client ourselves. So, convert the code to use a temporary
client and use the block-write function of the I2C core.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Asmaa Mnebhi <asmaa@nvidia.com>
Acked-by: Corey Minyard <cminyard@mvista.com>
Message-Id: <20210128085544.7609-1-wsa+renesas@sang-engineering.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>