fru: ops: Return error from checksum if data is all zero's

fru: ops: Return error from checksum if data is all zero's

fru_checksum function is simply adding all the bytes and returning the
sum. If the data passed to this function is all zero's then it will
return 0, and the functions calling this api will assume that checksum
is correct. Ideally this is not good. Fix this by returning error if all
the data is 0's.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/ac0366fe55c60a818a3f9ed33d96826c817d5520.1645624855.git.michal.simek@xilinx.com