fpga: mgr: kernel-doc fixes

Clean up the kernel-doc documentation in fpga-mgr.c and fix the
following warnings when documentation is built:

./drivers/fpga/fpga-mgr.c:252: warning: Function parameter or member
'info' not described in 'fpga_mgr_buf_load'

./drivers/fpga/fpga-mgr.c:252: warning: Excess function parameter
'flags' description in 'fpga_mgr_buf_load'

Signed-off-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>