wifi: p54: fix GCC format truncation warning with wiphy->fw_version

GCC 13.2 warns:

drivers/net/wireless/intersil/p54/fwio.c:128:34: warning: '%s' directive output may be truncated writing up to 39 bytes into a region of size 32 [-Wformat-truncation=]
drivers/net/wireless/intersil/p54/fwio.c:128:33: note: directive argument in the range [0, 16777215]
drivers/net/wireless/intersil/p54/fwio.c:128:33: note: directive argument in the range [0, 255]
drivers/net/wireless/intersil/p54/fwio.c:127:17: note: 'snprintf' output between 7 and 52 bytes into a destination of size 32

The issue here is that wiphy->fw_version is 32 bytes and in theory the string
we try to place there can be 39 bytes. wiphy->fw_version is used for providing
the firmware version to user space via ethtool, so not really important.
fw_version in theory can be 24 bytes but in practise it's shorter, so even if
print only 19 bytes via ethtool there should not be any practical difference.

I did consider removing fw_var from the string altogether or making the maximum
length for fw_version 19 bytes, but chose this approach as it was the least
intrusive.

Compile tested only.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Acked-by: Christian Lamparter <chunkeey@gmail.com> # Tested with Dell 1450 USB
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20231219162516.898205-1-kvalo@kernel.org