ANDROID: drivers/misc: disable LTO for rodata.o

LKDTM was refactored in 4.17 and lkdtm_rodata.o was moved to
lkdtm/rodata.o. Fix CFLAGS to apply to the correct object file,
so LKDTM can be built with LTO.

Bug: 133186739
Change-Id: I906db4aecabf42dec905a8b03933689732ab5b52
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>