lzma: Fix compilation error under clang 10

lzma: Fix compilation error under clang 10

Compiling under clang 10 gives:

grub-core/lib/LzmaEnc.c:1362:9: error: misleading indentation; statement is not part of the previous 'if' [-Werror,-Wmisleading-indentation]
        {
        ^
grub-core/lib/LzmaEnc.c:1358:7: note: previous statement is here
      if (repIndex == 0)
      ^
1 error generated.

It's not really that unclear in context: there's a commented-out
if-statement. But tweak the alignment anyway so that clang is happy.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>