hw/sd/sdhci: Fix qemu_log_mask() format string

Add missing newline character in qemu_log_mask() format.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200901140411.112150-2-f4bug@amsat.org>