raw/ifpga/base: check lseek failure
raw/ifpga/base: check lseek failure

In write_flash_image(), calling function "lseek" without checking
return value has risk. Negative return value should be handled as
an error condition.

Coverity issue: 367478
Fixes: a05bd1b40bde ("raw/ifpga: add FPGA RSU APIs")

Signed-off-by: Wei Huang <89cc104c2b51ed5072a0e69d914f07ce31ddcd43@intel.com>
Acked-by: Tianfei Zhang <2a67acadc8f062c05decf7f3cfb8392d35aa1752@intel.com>
Acked-by: Rosen Xu <8f603db01337dbfe2ce4743ebc0cdbcec6fa456f@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk