Drop the "-x lzo" compression type override from MKUBIFS_OPTS since we
do not support it in mkfs.ubifs. Attempting to use LZO compression results
in "Error: bad compressor name".
The build system also appends an explicit "--compr=zlib" to the mkfs command
line, turning the "-x" flag into a no-op anyway.
Signed-off-by: Jo-Philipp Wich <jo@mein.io>