binfmt_elf: remove unused argument in fill_elf_header

In fill_elf_header(), elf->e_ident[EI_OSABI] is always set to ELF_OSABI,
so remove the unused argument 'osabi'.

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>