spi: omap3: Fix redeclared error

omap3_spi_set_speed|mode redeclared bus symbol, fix the same.

error:
drivers/spi/omap3_spi.c: In function ‘omap3_spi_set_speed’:
drivers/spi/omap3_spi.c:650:18: error: ‘bus’ redeclared as different kind of symbol
  struct udevice *bus = dev->parent;

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>