brcmfmac: allow NVRAM values to contain spaces

Platform NVRAMs often contain values with spaces. Even if right now most
firmware-supported entries are simple values, we shouldn't reject these
with spaces. It was semi-confirmed by Broadcom in the early patch adding
support for platform NVRAMs.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>