USB: ice40-hcd: Increase retry for loading firmware to 8

Increase retry for loading firmware to 8, so that firmware load is tried
for 8 times before it fails loading of modules. If loading of firmware
fails for 8 times consecutively then this exits returning error code.

CRs-fixed: 670998
Change-Id: I0e26f31c78e1ff47448b466d3b665b9c5a09f4e7
Signed-off-by: Tarun Gupta <tarung@codeaurora.org>