cpu stm32f1 periph spi: simplify condition

boards/spark-core/system_stm32f1.c

@@ -41,7 +41,7 @@ static void set_system_clock(void)
     }
     while ((HSE_status == 0) && (startup_counter != HSE_STARTUP_TIMEOUT));
 
-    if ((RCC->CR & RCC_CR_HSERDY) != RESET) {
+    if (!(RCC->CR & RCC_CR_HSERDY)) {
         HSE_status = (uint32_t)0x01;
     }
     else {

cpu/stm32f1/periph/spi.c

@@ -207,11 +207,11 @@ int spi_transfer_byte(spi_t dev, char out, char *in)
             return -1;
     }
 
-    while ((spi->SR & SPI_SR_TXE) == RESET);
+    while (!(spi->SR & SPI_SR_TXE));
     spi->DR = out;
     transferred++;
 
-    while ((spi->SR & SPI_SR_RXNE) == RESET);
+    while (!(spi->SR & SPI_SR_RXNE));
     if (in != NULL) {
         *in = spi->DR;
         transferred++;