bnx2x: Fix firmware version string character counts

A potential string truncation was reported in bnx2x_fill_fw_str(),
when a long bp->fw_ver and a long phy_fw_ver might coexist, but seems
unlikely with real-world hardware.

Use scnprintf() to indicate the intent that truncations are tolerated.

While reading this code, I found a collection of various buffer size
counting issues. None looked like they might lead to a buffer overflow
with current code (the small buffers are 20 bytes and might only ever
consume 10 bytes twice with a trailing %NUL). However, early truncation
(due to a %NUL in the middle of the string) might be happening under
likely rare conditions. Regardless fix the formatters and related
functions:

- Switch from a separate strscpy() to just adding an additional "%s" to
the format string that immediately follows it in bnx2x_fill_fw_str().
- Use sizeof() universally instead of using unbound defines.
- Fix bnx2x_7101_format_ver() and bnx2x_null_format_ver() to report the
number of characters written, not including the trailing %NUL (as
already done with the other firmware formatting functions).
- Require space for at least 1 byte in bnx2x_get_ext_phy_fw_version()
for the trailing %NUL.
- Correct the needed buffer size in bnx2x_3_seq_format_ver().

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401260858.jZN6vD1k-lkp@intel.com/
Cc: Ariel Elior <aelior@marvell.com>
Cc: Sudarsana Kalluru <skalluru@marvell.com>
Cc: Manish Chopra <manishc@marvell.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240126041044.work.220-kees@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>