staging: comedi: ke_counter: prefer using the BIT macro

Use a macro to define the clock source options. This fixes the
checkpatch.pl issue about:

CHECK: Prefer using the BIT macro
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/ke_counter.c

@@ -41,9 +41,10 @@
 #define KE_MSB_REG(x)			(0x0c + ((x) * 0x20))
 #define KE_SIGN_REG(x)			(0x10 + ((x) * 0x20))
 #define KE_OSC_SEL_REG			0xf8
-#define KE_OSC_SEL_EXT			(1 << 0)
-#define KE_OSC_SEL_4MHZ			(2 << 0)
-#define KE_OSC_SEL_20MHZ		(3 << 0)
+#define KE_OSC_SEL_CLK(x)		(((x) & 0x3) << 0)
+#define KE_OSC_SEL_EXT			KE_OSC_SEL_CLK(1)
+#define KE_OSC_SEL_4MHZ			KE_OSC_SEL_CLK(2)
+#define KE_OSC_SEL_20MHZ		KE_OSC_SEL_CLK(3)
 #define KE_DO_REG			0xfc
 
 static int ke_counter_insn_write(struct comedi_device *dev,