x86/Makefile: Remove unneeded whitespaces before tabs

Align the FDINITRD line to the FDARGS one with tabs.

 [ bp: Commit message. ]

Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211028121021.10384-1-ehaouas@noos.fr