brcmfmac: fix CLM load error for legacy chips when user helper is enabled

For legacy chips without CLM blob files, kernel with user helper function
returns -EAGAIN when we request_firmware(), and then driver got failed
when bringing up legacy chips. We expect the CLM blob file for legacy chip
is not existence in firmware path, but the -ENOENT error is transferred to
-EAGAIN in firmware_class.c with user helper.
Because of that, we continue with CLM data currently present in firmware
if getting error from doing request_firmware().

Cc: stable@vger.kernel.org # v4.15.y
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>