rtc: rc5t619: Fix an ERR_PTR vs NULL check

rtc: rc5t619: Fix an ERR_PTR vs NULL check

[ Upstream commit 11ddbdfb68e4f9791e4bd4f8d7c87d3f19670967 ]

The devm_kzalloc() function returns NULL on error, it doesn't return
error pointers so this check doesn't work.

Fixes: 540d1e15393d ("rtc: rc5t619: Add Ricoh RC5T619 RTC driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20200407092852.GI68494@mwanda
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>