gdb/linux-nat: check ptrace return value in linux_nat_get_siginfo

Not a big deal, but it seems strange to check errno instead of the
ptrace return value to know whether it succeeded.

Change-Id: If0a6d0280ab0e5ecb077e546af0d6fe489c5b9fd

gdb/linux-nat.c

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index c47b8db..b33fac3 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4443,11 +4443,7 @@ bool
 linux_nat_get_siginfo (ptid_t ptid, siginfo_t *siginfo)
 {
   int pid = get_ptrace_pid (ptid);
-
-  errno = 0;
-  ptrace (PTRACE_GETSIGINFO, pid, (PTRACE_TYPE_ARG3) 0, siginfo);
-
-  return errno == 0;
+  return ptrace (PTRACE_GETSIGINFO, pid, (PTRACE_TYPE_ARG3) 0, siginfo) == 0;
 }
 
 /* See nat/linux-nat.h.  */