stm32/sdcard: Don't use SD clock bypass on F7 MCUs.

With clock bypass enabled the attached SD card is clocked at the maximum
48MHz.  But some SD cards are unreliable at these rates.  Although it's
nice to have high speed transfers it's more important that the transfers
are reliable for all cards.  So disable this clock bypass option.

ports/stm32/sdcard.c

@@ -222,10 +222,6 @@ bool sdcard_power_on(void) {
     }
 
     // configure the SD bus width for wide operation
-    #if defined(STM32F7)
-    // use maximum SDMMC clock speed on F7 MCUs
-    sd_handle.Init.ClockBypass = SDMMC_CLOCK_BYPASS_ENABLE;
-    #endif
     if (HAL_SD_ConfigWideBusOperation(&sd_handle, SDIO_BUS_WIDE_4B) != HAL_OK) {
         HAL_SD_DeInit(&sd_handle);
         goto error;