secure: Add ssh-sk-client to all consumers of libssh

These all failed to link with ld.bfd used by GCC due to
Fssh_sshsk_sign being an unresolved symbol.

Fixes:		65d8491719 ("secure: Adapt Makefile to ssh-sk-client everywhere")

secure/libexec/sftp-server/Makefile

@@ -2,7 +2,7 @@
 .include "${SRCTOP}/secure/ssh.mk"
 
 PROG=	sftp-server
-SRCS=	sftp-common.c sftp-server.c sftp-server-main.c
+SRCS=	sftp-common.c sftp-server.c sftp-server-main.c $(SKSRCS)
 MAN=	sftp-server.8
 
 LIBADD=	ssh

secure/usr.bin/scp/Makefile

@@ -2,7 +2,7 @@
 .include "${SRCTOP}/secure/ssh.mk"
 
 PROG=	scp
-SRCS=	scp.c progressmeter.c $(SFTP_CLIENT_SRCS)
+SRCS=	scp.c progressmeter.c $(SFTP_CLIENT_SRCS) $(SKSRCS)
 PACKAGE=	ssh
 
 LIBADD=	ssh

secure/usr.bin/sftp/Makefile

@@ -2,7 +2,7 @@
 .include "${SRCTOP}/secure/ssh.mk"
 
 PROG=	sftp
-SRCS=	sftp.c sftp-usergroup.c progressmeter.c $(SFTP_CLIENT_SRCS)
+SRCS=	sftp.c sftp-usergroup.c progressmeter.c $(SFTP_CLIENT_SRCS) $(SKSRCS)
 PACKAGE=	ssh
 
 LIBADD=	ssh edit