buildroot

fs/ext2: fix typo

BR2_TARGET_ROOTFS_EXT2_RESBLKS is an int, so test against 0 rather than
the empty string - Otherwise the test is always true and a -m option
without arguments is added to the argument list, causing genext2fs to
get confused.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>