i2c: zx2967: drop COMPILE_TEST dependency

i2c: zx2967: drop COMPILE_TEST dependency

0-DAY kernel test reports the following build issue on IA64 architecture
with allmodconfig.

   drivers/i2c/busses/i2c-zx2967.c: In function 'zx2967_i2c_writesb':
>> drivers/i2c/busses/i2c-zx2967.c:87:2: error: implicit declaration of function 'writesb' [-Werror=implicit-function-declaration]
     writesb(i2c->reg_base + reg, data, len);
     ^~~~~~~
   drivers/i2c/busses/i2c-zx2967.c: In function 'zx2967_i2c_readsb':
>> drivers/i2c/busses/i2c-zx2967.c:93:2: error: implicit declaration of function 'readsb' [-Werror=implicit-function-declaration]
     readsb(i2c->reg_base + reg, data, len);
     ^~~~~~
   cc1: some warnings being treated as errors

It's caused by that writesb/readsb are unavailable on IA64 architecture.
Let's drop COMPILE_TEST dependency to avoid the build issue.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>