pmic: fsl: Define number of bytes sent at once by MC34708 PMIC

This patch adds definition of the number of bytes sent at once by the
MC34708 PMIC.

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/fsl_pmic.h

@@ -156,4 +156,5 @@ enum {
 #define SW_MODE_PWMPFM		0x0d
 #define SW_MODE_PFMPFM		0x0f
 
+#define MC34708_TRANSFER_SIZE 3
 #endif