gitignore: remove stale /LOG pattern

The /LOG directory was created by the old MAKEALL tool, which was
deleted by commit c8a3777c ("Drop the MAKEALL tool").
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

.gitignore

@@ -48,7 +48,6 @@ fit-dtb.blob
 #
 # Generated files
 #
-/LOG
 /spl/
 /tpl/
 /defconfig