spi: davinci: eliminate unnecessary update of davinci_spi->count

The count member of davinci_spi is internal to the driver and
is not shared with framework. Eliminate its unnecessary update.

Signed-off-by: Brian Niebuhr <bniebuhr@efjohnson.com>
Tested-By: Michael Williamson <michael.williamson@criticallink.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>