brcmfmac: reduce log level in fwil if firmware returns error

The users of the fwil put an error message in the log so there is
no need to do the same in the lower level functions in fwil when
the firmware on the device returns an error. Some errors can be
ignored for the driver to function and this will avoid driver users
to point at the low-level error message as potential bug.

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: John W. Linville <linville@tuxdriver.com>
Merge pull request #14 from linux4kix/linux-linaro-lsk-v3.14-mx6

brcmfmac: reduce log level in fwil if firmware returns error