spi: davinci: remove unnecessary 'count' variable in driver private data

The variable count in DaVinci SPI driver's private data is
largely unused and its minor use can easily be eliminated.

Remove the variable.

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