watchdog: coh901327: add COMMON_CLK dependency

clang produces a build failure in configurations without COMMON_CLK
when a timeout calculation goes wrong:

arm-linux-gnueabi-ld: drivers/watchdog/coh901327_wdt.o: in function `coh901327_enable':
coh901327_wdt.c:(.text+0x50): undefined reference to `__bad_udelay'

Add a Kconfig dependency to only do build testing when COMMON_CLK
is enabled.

Fixes: da2a68b3 ("watchdog: Enable COMPILE_TEST where possible")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201203223358.1269372-1-arnd@kernel.org


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>