Fix incorrect integer division in analogout_read

Replace with multiplication by the floating point reciprocal, to
 produce a floating point result while being more efficient than
 floating point division.
Addresses the issue raised by kjbracey-arm in
https://github.com/ARMmbed/mbed-os/pull/11324#pullrequestreview-282433989

targets/TARGET_Cypress/TARGET_PSOC6/cy_analogout_api.c

@@ -51,7 +51,7 @@ void analogout_write_u16(dac_t *obj, uint16_t value)
 
 float analogout_read(dac_t *obj)
 {
-    return analogout_read_u16(obj) / UINT16_MAX;
+    return analogout_read_u16(obj) * (1.0f / UINT16_MAX);
 }
 
 uint16_t analogout_read_u16(dac_t *obj)