ixgbe: Fix an error handling path in ixgbe_read_iosf_sb_reg_x550()

All error handling paths, except this one, go to 'out' where
release_swfw_sync() is called.
This call balances the acquire_swfw_sync() call done at the beginning of
the function.

Branch to the error handling path in order to correctly release some
resources in case of error.

Fixes: ae14a1d8

 ("ixgbe: Fix IOSF SB access issues")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>