sdcard: Reduce sdcard_set_blocklen() trace digits

Per the Physical Layer Simplified Spec. "5.3 CSD Register":

  "The maximum block length might therefore be in the range 512...2048 bytes"

Therefore 3 hexdigits are enough to report the block length.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/sd/trace-events

@@ -37,7 +37,7 @@ sdcard_powerup(void) ""
 sdcard_inquiry_cmd41(void) ""
 sdcard_set_enable(bool current_state, bool new_state) "%u -> %u"
 sdcard_reset(void) ""
-sdcard_set_blocklen(uint16_t length) "0x%04x"
+sdcard_set_blocklen(uint16_t length) "0x%03x"
 sdcard_inserted(bool readonly) "read_only: %u"
 sdcard_ejected(void) ""
 sdcard_erase(void) ""