lib/lzo: Rename lzo1x_decompress.c to lzo1x_decompress_safe.c

Rename the source file to match the function name and thereby
also make room for a possible future even slightly faster
non-safe decompressor version.

Change-Id: I482ee415d43c5aaa77d34946ae1fa0af5465b007
Signed-off-by: Markus F.X.J. Oberhumer <markus@oberhumer.com>