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: Ic6551cf65f1909e288b3857e841980a56a8c59b6
Signed-off-by: Markus F.X.J. Oberhumer <markus@oberhumer.com>