Calling spa_open() will pass a NULL pointer to spa_open_common()'s
config parameter. Under the right circumstances, we will dereference the
config parameter without doing a NULL check.
Clang's static analyzer found this.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes#14044