wil6210: add block size checks during FW load

When loading FW from file add block size checks to ensure a
corrupted FW file will not cause the driver to write outside
the device memory.

Signed-off-by: Lior David <qca_liord@qca.qualcomm.com>
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>