wifi: brcmfmac: fix format-truncation warnings

On v6.6-rc4 with GCC 13.2 I see:

drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:262:52: warning: '%d' directive output may be truncated writing between 1 and 5 bytes into a region of size 4 [-Wformat-truncation=]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:262:46: note: directive argument in the range [0, 65535]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:262:46: note: directive argument in the range [0, 65535]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:262:9: note: 'snprintf' output between 9 and 17 bytes into a destination of size 9
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:265:55: warning: '%d' directive output may be truncated writing between 1 and 5 bytes into a region of size 4 [-Wformat-truncation=]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:265:48: note: directive argument in the range [0, 65535]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:265:48: note: directive argument in the range [0, 65535]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:265:9: note: 'snprintf' output between 10 and 18 bytes into a destination of size 10
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:342:50: warning: '/' directive output may be truncated writing 1 byte into a region of size between 0 and 4 [-Wformat-truncation=]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:342:42: note: directive argument in the range [0, 65535]
drivers/net/wireless/broadcom/brcm80211/brcmfmac/firmware.c:342:9: note: 'snprintf' output between 10 and 18 bytes into a destination of size 10

Fix these by increasing the buffer sizes to 20 bytes to make sure there's enough space.

Compile tested only.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231012135854.3473332-1-kvalo@kernel.org