soc/amd/stoneyridge/southbridge.c: Fix get_index_bit limit check

Limit is the maximum number of bits to be tested, however it's being checked
against the number of bytes of uint32_t. when it should be number of bits.
Create a macro to provide the number of bits, and use it instead of sizeof.

BUG=b:75996437
TEST=Add debug messages to see code passing beyond the check, build and
boot grunt, check that it passed the limit check, remove debug code.

Change-Id: Id1dfda26d789183b346b20c37fec923d996b80db
Signed-off-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-on: https://review.coreboot.org/27162
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
2 files changed