broadcom_wl: eliminate compiler error with gcc-4.9-linaro

Attempting to build broadcom_wl (from trunk) with the linaro 4.9.x
toolchain produces the following errors:

<...>/wl_linux.c: In function 'wl_dump_ver':
<...>/wl_linux.c:2302:3: error: macro "__DATE__" might prevent reproducible builds [-Werror=date-time]
   __DATE__, __TIME__, EPI_VERSION_STR);
   ^
<...>/wl_linux.c:2302:13: error: macro "__TIME__" might prevent reproducible builds [-Werror=date-time]
   __DATE__, __TIME__, EPI_VERSION_STR);
             ^
cc1: some warnings being treated as errors

Remove the use of the __DATE__ and __TIME__ macros, as the info is not
really useful.

Signed-off-by: Nathan Hintz <nlhintz@hotmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43046 3c298f89-4303-0410-b956-a3cf2f4a3e73