i3c: master: Fix an error checking typo in 'cdns_i3c_master_probe()'

Fix a cut'n'paste typo.
Checking 'master->sysclk' is expected here.

Fixes: 603f2bee ("i3c: master: Add driver for Cadence IP")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>