Cypress: Fix unitialized memory in spi_master_write

'received' was declared as an int but populated by cyhal_spi_transfer
after being cast to to (uint8_t *), which left the upper 3 bytes
uninitialized. Instead, declare as uint8_t and let the compiler upcast
the value when it is returned.

Author: Kyle Kearney

targets/TARGET_Cypress/TARGET_PSOC6/cy_spi_api.c

@@ -140,9 +140,9 @@ void spi_frequency(spi_t *obj, int hz)
 int spi_master_write(spi_t *obj, int value)
 {
     struct spi_s *spi = cy_get_spi(obj);
-    int received;
+    uint8_t received;
 
-    if (CY_RSLT_SUCCESS != cyhal_spi_transfer(&(spi->hal_spi), (const uint8_t *)&value, 1, (uint8_t *)&received, 1, 0xff)) {
+    if (CY_RSLT_SUCCESS != cyhal_spi_transfer(&(spi->hal_spi), (const uint8_t *)&value, 1, &received, 1, 0xff)) {
         MBED_ERROR(MBED_MAKE_ERROR(MBED_MODULE_DRIVER_SPI, MBED_ERROR_CODE_FAILED_OPERATION), "cyhal_spi_transfer");
     }
     return received;