fix build warnings

Hi!

Attached patch fixes build warnings due to use of different pointer
signedness.

Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>

--
---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Karl-Hammerschmidt-Str. 34, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Thomas M. McCoy, Giuliano Meroni
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632
diff --git a/bsd-user/uaccess.c b/bsd-user/uaccess.c
index 9ec1b23..677f19c 100644
--- a/bsd-user/uaccess.c
+++ b/bsd-user/uaccess.c
@@ -51,7 +51,7 @@
         ptr = lock_user(VERIFY_READ, guest_addr, max_len, 1);
         if (!ptr)
             return -TARGET_EFAULT;
-        len = qemu_strnlen(ptr, max_len);
+        len = qemu_strnlen((char *)ptr, max_len);
         unlock_user(ptr, guest_addr, 0);
         guest_addr += len;
         /* we don't allow wrapping or integer overflow */