ice1usb: define e1_data_ptr() using e1_data_ofs()

It's best to compute the offset only at one place and use that
computation elsewhere.

Change-Id: I9a6cce07ea8b6eff1527215de00621da960b0472
diff --git a/firmware/ice40-riscv/icE1usb/e1.c b/firmware/ice40-riscv/icE1usb/e1.c
index e5108ce..776edba 100644
--- a/firmware/ice40-riscv/icE1usb/e1.c
+++ b/firmware/ice40-riscv/icE1usb/e1.c
@@ -80,19 +80,17 @@
 static volatile struct e1_core * const e1_regs = (void *)(E1_CORE_BASE);
 static volatile uint8_t * const e1_data = (void *)(E1_DATA_BASE);
 
-
-volatile uint8_t *
-e1_data_ptr(int mf, int frame, int ts)
-{
-	return &e1_data[(mf << 9) | (frame << 5) | ts];
-}
-
 unsigned int
 e1_data_ofs(int mf, int frame, int ts)
 {
 	return (mf << 9) | (frame << 5) | ts;
 }
 
+volatile uint8_t *
+e1_data_ptr(int mf, int frame, int ts)
+{
+	return &e1_data[e1_data_ofs(mf, frame, ts)];
+}
 
 // FIFOs
 // -----