Documentation: Fix make rule for sphinx-autobuild

Execute sphinx-autobuild for livesphinx make rule

Change-Id: I725392f1f132101eede8fed75e8d225c972ad1fe
Signed-off-by: Tom Hiller <thrilleratplay@gmail.com>
Reviewed-on: https://review.coreboot.org/28326
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
1 file changed