target/m68k/helper: Fix m68k_fpu_gdb_get_reg() use of GByteArray

Since a010bdbe719 the gdbstub API takes a GByteArray*. Unfortunately
we forgot to update the gdb_get_reg*() calls. Do it now.

Fixes: a010bdbe719 ("extend GByteArray to read register helpers")
Reported-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200409172509.4078-1-philmd@redhat.com>
Message-Id: <20200414200631.12799-11-alex.bennee@linaro.org>
diff --git a/target/m68k/helper.c b/target/m68k/helper.c
index 014657c..cad4083 100644
--- a/target/m68k/helper.c
+++ b/target/m68k/helper.c
@@ -109,8 +109,8 @@
 {
     if (n < 8) {
         int len = gdb_get_reg16(mem_buf, env->fregs[n].l.upper);
-        len += gdb_get_reg16(mem_buf + len, 0);
-        len += gdb_get_reg64(mem_buf + len, env->fregs[n].l.lower);
+        len += gdb_get_reg16(mem_buf, 0);
+        len += gdb_get_reg64(mem_buf, env->fregs[n].l.lower);
         return len;
     }
     switch (n) {