tty: serial: make SERIAL_SPRD depend on COMMON_CLK

kbuild-test reported an error:

  config: mips-randconfig-a001-20200321 ...
  >> drivers/tty/serial/sprd_serial.c:1175: undefined reference
  to `clk_set_parent'

Because some mips Kconfig selects HAVE_CLK but not COMMON_CLK and no
clk_set_parent implemented, so the error was exposed. So adding
dependence on COMMON_CLK can fix this issue.

Fixes: 7ba87cfe ("tty: serial: make SERIAL_SPRD not depend on ARCH_SPRD")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lore.kernel.org/r/20200325081427.20312-1-zhang.lyra@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -1445,6 +1445,7 @@ config SERIAL_MEN_Z135
 config SERIAL_SPRD
 	tristate "Support for Spreadtrum serial"
 	select SERIAL_CORE
+	depends on COMMON_CLK
 	help
 	  This enables the driver for the Spreadtrum's serial.