fpga manager: Fix firmware resource leak on error

If fpga_mgr_buf_load() fails, the firmware resource previously allocated
by request_firmware() is leaked. Fix it by calling release_firmware()
regardless of the return value of fpga_mgr_buf_load().

Found by the Coverity scanner (CID 1339653).

Fixes: 6a8c3be7 ("add FPGA manager core")
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Alan Tull <atull@opensource.altera.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>