leds: renesas: fix error handling

bfe4c041 "leds: convert Renesas TPU LED driver to devm_kzalloc() and
cleanup error exit path" introduced a possible case in which r_tpu_probe
calls iounmap on a wild pointer. This changes the one case that was
missed in the same way as the other error paths.

Without this patch, building kota2_defconfig results in:

drivers/leds/leds-renesas-tpu.c: In function 'r_tpu_probe':
drivers/leds/leds-renesas-tpu.c:246:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized]
drivers/leds/leds-renesas-tpu.c:308:17: warning: 'p' may be used uninitialized in this function [-Wuninitialized]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Magnus Damm <damm@opensource.se>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>