brcm80211: util: remove function brcmu_format_hex() from brcmutil

The function brcmu_format_hex() filled a string buffer with byte
values from a data buffer. The calling function used this string
buffer in a printk. Now the calling function uses the kernel
function print_hex_dump_bytes().

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>