brcmfmac: Don't promote INFO logging to ERR

An unwanted side effect of enabling the BRCMDBG config setting is
redefining brcmf_info to be brcmf_err. This can be alarming to users
and makes it harder to spot real errors, so don't do it.

See: https://github.com/raspberrypi/linux/issues/4663



Signed-off-by: Phil Elwell <phil@raspberrypi.com>