fsl_i2c: Fix compile warning

fsl_i2c.c: In function 'i2c_init':
fsl_i2c.c:245:7: warning: assignment discards qualifiers from pointer target type

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

drivers/i2c/fsl_i2c.c

@@ -225,7 +225,7 @@ unsigned int get_i2c_clock(int bus)
 void
 i2c_init(int speed, int slaveadd)
 {
-	struct fsl_i2c *dev;
+	const struct fsl_i2c *dev;
 	unsigned int temp;
 	int bus_num, i;