linux-user: Fix ioctl cmd type mismatch on 64-bit targets

linux-user passes the cmd argument of the ioctl syscall as a signed long,
but compares it to an unsigned int when iterating through the ioctl_entries
list.  When the cmd is a large value like 0x80047476 (TARGET_TIOCSWINSZ on
mips64) it gets sign-extended to 0xffffffff80047476, causing the comparison
to fail and resulting in lots of spurious "Unsupported ioctl" errors.
Changing the target_cmd field in the ioctl_entries list to a signed int
causes those values to be sign-extended as well during the comparison.

Signed-off-by: Ed Swierk <eswierk@skyportsystems.com>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5658b66..683f8cc 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -3278,7 +3278,7 @@
                              int fd, abi_long cmd, abi_long arg);
 
 struct IOCTLEntry {
-    unsigned int target_cmd;
+    int target_cmd;
     unsigned int host_cmd;
     const char *name;
     int access;