brcmutil: use define for boardrev string function

Introducing a define that the caller of brcmu_boardrev_str() can
use to allocate enough room for buffer passed to the function.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/brcm80211/include/brcmu_utils.h

@@ -218,6 +218,8 @@ void brcmu_dbg_hex_dump(const void *data, size_t size, const char *fmt, ...)
 }
 #endif
 
+#define BRCMU_BOARDREV_LEN	8
+
 char *brcmu_boardrev_str(u32 brev, char *buf);
 
 #endif				/* _BRCMU_UTILS_H_ */