be2net: Fix smatch warnings in be_main.c

FW flashing code, even though it works correctly, makes some hidden
assumptions about buffer sizes. This is causing code analysers to
report error. Cleanup FW flashing code to remove these hidden assumptions.

Reported-by: Yuanhan Liu <yuanhan.liu@intel.com>
Signed-off-by: Vasundhara Volam <vasundhara.volam@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: Padmanabh Ratnakar <padmanabh.ratnakar@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>