perf/x86/intel/ds: Check return values of insn decoder functions

branch_type() doesn't need to call the full insn_decode() because it
doesn't need it in all cases thus leave the calls separate.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210304174237.31945-9-bp@alien8.de