i2c: ismt: initialize DMA buffer

commit bf4169100c909667ede6af67668b3ecce6928343 upstream.

This patch adds code to initialize the DMA buffer to compensate for
possible hardware data corruption.

Signed-off-by: James Ralston <james.d.ralston@intel.com>
[wsa: changed to use 'sizeof']
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>