mwlwifi: use PKG_SOURCE_DATE instead of version

Using PKG_SOURCE_DATE instead of PKG_VERSION will make the build system
generate the version based on the date and the git hash. This way the
tar file name changes when the git hash changes and this avoids problems
when someone forgets to change the version, but changes the git hash.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/kernel/mwlwifi/Makefile

@@ -8,7 +8,6 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mwlwifi
-PKG_VERSION:=10.3.4.0-20180208
 PKG_RELEASE=1
 
 PKG_LICENSE:=ISC
@@ -16,8 +15,9 @@ PKG_LICENSE_FILES:=
 
 PKG_SOURCE_URL:=https://github.com/kaloz/mwlwifi
 PKG_SOURCE_PROTO:=git
+PKG_SOURCE_DATE:=2018-02-08
 PKG_SOURCE_VERSION:=064e888e801d5e4c3638e92ee18a2cde06a6f2d0
-PKG_MIRROR_HASH:=606c66a458c65b572d73c56bd9e69ec9c45a5c989c17442ebd3076dd76f2aea2
+PKG_MIRROR_HASH:=9214ffcf43781c71a9d13baa0d515d8d3f64c5f853636b186b9633af286e443a
 
 PKG_MAINTAINER:=Imre Kaloz <kaloz@openwrt.org>
 PKG_BUILD_PARALLEL:=1