package/strace: fix nios2_sp_ptr definition

The patch [1] introduced in strace 1.17 uses the old way of accessing
SP register as defined for kernel headers < 4.0. The kernel headers
for nios2 has been changed in commit [2].

This patch updates strace to use the new kernel/userspace interface.

Fixes:
http://autobuild.buildroot.net/results/b9f/b9fc25b82f3280872fe1593ac252a8529ba83576

[1] https://github.com/strace/strace/commit/6117728aacf431a3e3c05761766c776874cc0861
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=92d5dd8cd6e2b211d32d8fbc6cf4b7470765a09f



Signed-off-by: Romain Naour <romain.naour@smile.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas: improve a bit the commit log and patch description.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>