brcmfmac: fix throughput zero stalls on PM 1 mode due to credit map

This patch move the credit map setting to right place to avoid
brcmf_fws_return_credits() return without setting the credit map.
It fix the thoughput zero stalls issue in softAP mode when STA
using PM 1 mode.

Signed-off-by: Double Lo <double.lo@cypress.com>
Signed-off-by: Chi-hsien Lin <chi-hsien.lin@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200610152106.175257-6-chi-hsien.lin@cypress.com