semihosting: Fix GDB File-I/O FLEN

fstat returns 0 on success and -1 on error. Since we have already
checked for error, ret must be zero. Therefore, any call to fstat on a
non-empty file will return -1/EOVERFLOW.

Restore the original logic that just did a byteswap. I don't really know
what the intention of the fixed commit was.

Fixes: a6300ed6b7 ("semihosting: Split out semihost_sys_flen")
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20251027110344.2289945-36-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

semihosting/arm-compat-semi.c

@@ -316,10 +316,7 @@ common_semi_flen_fstat_cb(CPUState *cs, uint64_t ret, int err)
                                 &size, 8, 0)) {
             ret = -1, err = EFAULT;
         } else {
-            size = be64_to_cpu(size);
-            if (ret != size) {
-                ret = -1, err = EOVERFLOW;
-            }
+            ret = be64_to_cpu(size);
         }
     }
     common_semi_cb(cs, ret, err);