hostapd: remove erroneous $(space) redefinition

hostapd: remove erroneous $(space) redefinition

The $(space) definition in the hostapd Makefile ceased to work with
GNU Make 4.3 and later, leading to syntax errors in the generated
Kconfig files.

Drop the superfluous redefinition and reuse the working $(space)
declaration from rules.mk to fix this issue.

Fixes: GH#2713
Ref: https://github.com/openwrt/openwrt/pull/2713#issuecomment-583722469
Reported-by: Karel Kočí <[email protected]>
Suggested-by: Jonas Gorski <[email protected]>
Tested-by: Shaleen Jain <[email protected]>
Signed-off-by: Jo-Philipp Wich <[email protected]>