package/sshfs: fix build with gcc 4.8

Fix build of sshfs 3.7.0 and gcc 4.8

Fixes:
 - http://autobuild.buildroot.org/results/2dbdc579c55543175716d5f739cabe2ad0864ed6



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>