tools: ynl: fix the header guard name for OVPN

Thorsten reports that after upgrading system headers from linux-next
the YNL build breaks. I typo'ed the header guard, _H is missing.

Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
Link: https://lore.kernel.org/59ba7a94-17b9-485f-aa6d-14e4f01a7a39@leemhuis.info
Fixes: 12b1965 ("tools: ynl: add missing header deps")
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Thorsten Leemhuis <linux@leemhuis.info>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250423220231.1035931-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

tools/net/ynl/Makefile.deps

@@ -27,7 +27,7 @@ CFLAGS_netdev:=$(call get_hdr_inc,_LINUX_NETDEV_H,netdev.h)
 CFLAGS_nl80211:=$(call get_hdr_inc,__LINUX_NL802121_H,nl80211.h)
 CFLAGS_nlctrl:=$(call get_hdr_inc,__LINUX_GENERIC_NETLINK_H,genetlink.h)
 CFLAGS_nfsd:=$(call get_hdr_inc,_LINUX_NFSD_NETLINK_H,nfsd_netlink.h)
-CFLAGS_ovpn:=$(call get_hdr_inc,_LINUX_OVPN,ovpn.h)
+CFLAGS_ovpn:=$(call get_hdr_inc,_LINUX_OVPN_H,ovpn.h)
 CFLAGS_ovs_datapath:=$(call get_hdr_inc,__LINUX_OPENVSWITCH_H,openvswitch.h)
 CFLAGS_ovs_flow:=$(call get_hdr_inc,__LINUX_OPENVSWITCH_H,openvswitch.h)
 CFLAGS_ovs_vport:=$(call get_hdr_inc,__LINUX_OPENVSWITCH_H,openvswitch.h)