spi/omap2: fix uninitialized variable

fixes below compilation warning.  The variable doesn't actual ever get
used uninitialized, but that's no reason to be sloppy.

drivers/spi/omap2_mcspi.c: In function 'omap2_mcspi_txrx_dma':
drivers/spi/omap2_mcspi.c:301: warning: 'elements' may be used uninitialized in this function
Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
[grant.likely: amended description]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/omap2_mcspi.c

@@ -298,7 +298,7 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
 	unsigned int		count, c;
 	unsigned long		base, tx_reg, rx_reg;
 	int			word_len, data_type, element_count;
-	int			elements;
+	int			elements = 0;
 	u32			l;
 	u8			* rx;
 	const u8		* tx;