brcmfmac: treat NULL character in NVRAM as separator

Platform NVRAM (stored on a flash partition) has entries separated by a
NULL (\0) char. Our parsing code switches from VALUE state to IDLE
whenever it meets a NULL (\0). When that happens our IDLE handler should
simply consume it and analyze whatever is placed ahead.

This fixes harmless warnings spamming debugging output:
[  155.165624] brcmfmac: brcmf_nvram_handle_idle warning: ln=1:col=20: ignoring invalid character
[  155.180806] brcmfmac: brcmf_nvram_handle_idle warning: ln=1:col=44: ignoring invalid character
[  155.195971] brcmfmac: brcmf_nvram_handle_idle warning: ln=1:col=63: ignoring invalid character

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>