hw/misc/bcm2835_property: Avoid overflow in OTP access properties

Coverity points out that in our handling of the property
RPI_FWREQ_SET_CUSTOMER_OTP we have a potential overflow.  This
happens because we read start_num and number from the guest as
unsigned 32 bit integers, but then the variable 'n' we use as a loop
counter as we iterate from start_num to start_num + number is only an
"int".  That means that if the guest passes us a very large start_num
we will interpret it as negative.  This will result in an assertion
failure inside bcm2835_otp_set_row(), which checks that we didn't
pass it an invalid row number.

A similar issue applies to all the properties for accessing OTP rows
where we are iterating through with a start and length read from the
guest.

Use uint32_t for the loop counter to avoid this problem. Because in
all cases 'n' is only used as a loop counter, we can do this as
part of the for(), restricting its scope to exactly where we need it.

Resolves: Coverity CID 1549401
Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240723131029.1159908-3-peter.maydell@linaro.org

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