sh: Fix up unsigned syscall_nr in SH-5 pt_regs.

syscall_nr is presently defined as unsigned in the SH-5 pt_regs,
while the syscall restarting code wants it to be signed. Fix this
up, and bring it in line with the other SH parts.
Reported-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/ptrace.h

@@ -9,7 +9,7 @@
 struct pt_regs {
 	unsigned long long pc;
 	unsigned long long sr;
-	unsigned long long syscall_nr;
+	long long syscall_nr;
 	unsigned long long regs[63];
 	unsigned long long tregs[8];
 	unsigned long long pad[2];