fpga: fpga-mgr: Fix spelling mistake "bitsream" -> "bitstream"

There is an spelling mistake in a dev_err message. Fix it.

Fixes: 3cc624be ("fpga: fpga-mgr: support bitstream offset in image buffer")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220624081409.14760-1-colin.i.king@gmail.com


[yilun.xu@intel.com: add the Fixes tag]
Signed-off-by: Xu Yilun <yilun.xu@intel.com>